Continuous Glucose Monitors (CGMs) for Beginners: How They Work, Pros, Cons, and What They Really Cost

If you’ve ever pricked your finger to check blood sugar, you know it’s not exactly fun—or convenient. Continuous glucose monitors (CGMs) promise something different: near real-time glucose readings, tracked all day and night, right on your phone or a small reader.

For people living with diabetes or closely monitoring their blood sugar for other reasons, CGMs can feel like a game-changer. But they also raise a lot of questions:

• How do CGMs actually work?
• Who typically uses them—and why?
• What are the pros and cons compared with traditional fingerstick meters?
• How much do CGMs really cost, with and without insurance?

This guide walks through the basics in clear, practical language so you can understand what CGMs do, what they don’t do, and which questions to bring to a healthcare professional.

What Is a Continuous Glucose Monitor (CGM)?

A continuous glucose monitor is a small medical device that tracks your glucose levels throughout the day and night. Instead of a one-time reading from a fingerstick, a CGM:

• Measures glucose from interstitial fluid (the fluid just under your skin)
• Sends updated readings every few minutes to a receiver, smartphone, or insulin pump
• Stores data that can be reviewed later or shared with a clinical team

Many people use CGMs as part of a broader approach to diabetes management, especially those who:

• Use insulin
• Want to track patterns, such as after meals or during exercise
• Have difficulty recognizing low blood sugar symptoms

CGMs do not replace medical judgment or clinical care. They are tools that can provide more information, which some people find helpful for making day-to-day decisions in collaboration with their care team.

How CGMs Work: From Sensor to Screen

Understanding how CGMs work can make them feel much less intimidating.

Main Components of a CGM System

While designs vary, most CGMs include three main parts:

1. Sensor

   • A tiny, flexible filament inserted under the skin (usually on the abdomen, upper arm, or sometimes thigh).
   • Tracks glucose levels in interstitial fluid.
   • Worn for several days or weeks, depending on the model.

2. Transmitter

   • A small reusable or disposable piece that sits on top of the sensor.
   • Sends glucose data wirelessly to a receiver or compatible device.

3. Receiver or Display Device

   • Can be a dedicated handheld reader, a smartphone app, or in some cases an insulin pump.
   • Shows current glucose value, trend arrows, and often graphs.
   • May allow setting alerts for high and low glucose levels.

What a CGM Actually Measures

CGMs measure glucose in the fluid around cells, not directly in the blood. This type of fluid lags behind blood glucose by a short time—often described as several minutes.

This delay is one reason why:

• CGM readings may not match a fingerstick value exactly at all times
• Fingerstick checks might still be needed in certain situations, such as when glucose is changing rapidly or when readings do not match how someone feels

The Data You See

On a typical CGM display, you might see:

• Current glucose value (e.g., 110 mg/dL)
• Trend arrow(s) showing whether glucose is rising, falling, or stable
• Graph of glucose over the past several hours
• Alerts if levels hit pre-set high or low thresholds

This helps many users go beyond a single snapshot and instead see patterns: what happens after breakfast, during a workout, or overnight.

Who Commonly Uses CGMs?

CGMs are most commonly used as part of diabetes care, but the reasons and patterns of use vary.

People Managing Diabetes

CGMs are often used by:

• People with type 1 diabetes
• People with type 2 diabetes who use insulin
• Some people with gestational diabetes or other forms of diabetes, depending on individual circumstances and care-team judgment

Some users wear a CGM continuously. Others may use it intermittently, for example:

• For a few weeks at a time to understand patterns
• During specific periods, such as pregnancy, medication changes, or exercise training

People Without Diabetes

There is growing interest in CGMs among individuals without diagnosed diabetes who are curious about:

• How their glucose responds to certain foods
• Sleep, stress, or exercise patterns

For people without diabetes, CGM use is an emerging area and may not always be clinically necessary or covered by insurance. Interpretation of data can also be more complex, and professional guidance is often helpful to avoid misinterpretation or unnecessary worry.

Key Benefits of Continuous Glucose Monitors

Many users describe CGMs as giving them more visibility and context around their glucose levels. Some of the commonly reported benefits include:

1. Fewer Fingersticks (in Many Cases)

Certain CGM systems are designed to work with minimal or no routine fingerstick calibrations once set up, although fingersticks may still be needed in specific circumstances. This can reduce:

• Physical discomfort from repeated finger pricks
• The inconvenience of carrying test strips, lancets, and meters all the time

However, traditional glucose meters still play a role, especially for confirming readings that do not match symptoms.

2. Real-Time Trends and Alerts

Instead of asking “What is my glucose right now?” a CGM often helps answer:

• Where has my glucose been?
• Where is it heading?

Trend arrows and graphs can help some users:

• Notice when levels are drifting up or down
• See how quickly changes are happening
• Receive alerts for lows or highs, sometimes even before symptoms begin

For people who have difficulty noticing low blood sugar, or who experience overnight changes, these alerts can be particularly valuable.

3. Insight Into Food, Exercise, and Daily Life

CGM data can make cause-and-effect relationships more visible. For example, users often observe:

• How quickly different types of meals affect glucose
• Whether a late-night snack keeps levels elevated
• How different forms of exercise (like walking vs. high-intensity activity) impact glucose patterns

This does not automatically dictate what someone should eat or how they should live, but it can inform discussions with healthcare professionals and help individuals understand their own bodies better.

4. Data Sharing and Remote Viewing

Many CGM systems allow data sharing with:

• Family members or caregivers
• Healthcare professionals

In some setups, a trusted person can receive alerts if glucose goes very low or very high. Some users appreciate this extra layer of oversight, especially for children, older adults, or individuals with unrecognized lows.

Potential Downsides and Limitations of CGMs

Despite the advantages, CGMs are not perfect or universally suitable. Some common drawbacks include:

1. Cost and Insurance Barriers

CGMs can be significantly more expensive than traditional blood glucose meters, especially without insurance coverage. Costs include:

• Sensors (replaced every 7–14 days or longer, depending on model)
• Transmitters (if separate, replaced every several months)
• Receivers or compatible devices (if not using a smartphone)

Coverage varies widely by:

• Country or region
• Type of insurance
• Diabetes type and treatment plan
• Medical documentation or prior authorization requirements

For some people, the out-of-pocket cost is the main barrier to consistent use.

2. Device Wear and Skin Issues

Wearing a device on the body all the time is not comfortable for everyone. Common concerns include:

• Skin irritation or adhesive allergies
• Sensors accidentally getting knocked off (for example, during sports or showering)
• Feeling self-conscious about a visible device

Some users adapt quickly; others find wearability a recurring challenge. Rotating sites, using barrier wipes, or different adhesive strategies may help, but individual experiences vary.

3. Accuracy Considerations

While modern CGMs are generally regarded as reasonably accurate for day-to-day use, some limitations are important to understand:

• Readings measure interstitial fluid, not blood, and can lag when glucose is changing rapidly.
• Dehydration, compression (lying directly on a sensor), or site issues can affect readings in some cases.
• Fingerstick confirmation is often recommended when readings:
  • Do not match how someone feels
  • Change very quickly
  • Are used to make certain critical decisions, depending on professional guidance

4. Data Overload and Anxiety

CGMs generate a lot of information. For some people, this is empowering. For others, it can feel:

• Overwhelming
• Stressful to see every spike or dip
• Emotionally triggering, especially if they feel judged by the numbers

Using CGM data constructively—rather than as a source of guilt—often benefits from clear goals and support from healthcare professionals, educators, or counselors.

5. Technical Issues

Like any digital device, CGMs can have occasional:

• Sensor failures or early loss of signal
• Connectivity issues between the transmitter and phone/receiver
• App or software glitches

Most manufacturers have support lines and replacement policies for problematic sensors, but technical hiccups can still be frustrating.

CGMs vs. Traditional Glucose Meters

Both CGMs and standard fingerstick meters are medical devices used to check glucose, but they serve different roles.

In practice, many people use both tools:

• CGM for continuous monitoring and trend awareness
• Glucose meter for occasional verification or backup

Which mix is appropriate depends on individual health status, treatment plan, preferences, and professional recommendations.

Common Features to Understand When Comparing CGMs

If you are trying to understand CGM options in general terms, several features commonly come up.

Sensor Wear Time

Sensors are approved for specific wear intervals, often ranging from about 1 to 2 weeks, and some are designed for longer use. Longer wear can:

• Reduce the number of insertions
• Potentially lower hassle and adhesive irritation

Shorter wear might:

• Require more frequent replacements
• Provide flexibility if someone has skin issues or dislikes long-term wear in one area

Calibration Needs

Some CGMs require periodic calibration using fingerstick readings, while others are factory-calibrated and designed to be used without routine fingersticks in most circumstances.

Key points to consider:

• Calibration can improve alignment with blood glucose in some cases
• It also adds extra time, effort, and the need for a meter and strips

Data Display and Apps

Features vary by system, but may include:

• Smartphone app with graphs and trend lines
• Customizable alerts (e.g., different thresholds during day and night)
• Data sharing with family, caregivers, or clinics
• Integration with certain insulin pumps or smart pens

The overall user experience—app design, notification style, and ease of reviewing past data—can influence how helpful the CGM feels in daily life.

Alarms and Alerts

Many CGMs allow you to set:

• Low glucose alerts (e.g., below a certain number)
• High glucose alerts
• Rate-of-change alerts (glucose rising or falling rapidly)

Some users appreciate very tight alert settings; others prefer fewer alarms to reduce “alarm fatigue.” Customization is often important.

What Do CGMs Cost?

Costs vary widely, but understanding the main cost components can make planning easier.

1. Sensors

Sensors are the most frequently replaced part of the system. Common patterns include:

• Replacement every 7–14 days, depending on the model
• Some sensors designed for longer wear periods

The retail price per sensor (before insurance or discounts) is often substantial, especially when added up over a month or year. With coverage or discount programs, the individual’s cost may be significantly lower.

2. Transmitter

Some CGM systems use a separate transmitter that:

• Snaps into the sensor
• Lasts for several months or longer
• Eventually needs replacement

Transmitter costs can be a notable part of the overall annual expense but are purchased less frequently than sensors.

3. Receiver or Reader

Not all users need a dedicated receiver if:

• Their CGM can connect directly to a smartphone they already own
• The system integrates with an insulin pump or other device they already use

If a separate receiver is needed, it usually has a one-time purchase cost, sometimes with occasional upgrades.

4. Indirect Costs

Additional considerations may include:

• Adhesive patches or covers for extra security
• Skin barrier wipes or creams if irritation occurs
• Accessories like cases or armbands

These are often smaller expenses but can add up over time.

Insurance Coverage and Out-of-Pocket Costs

Because there is no single standard worldwide, coverage for CGMs is highly variable. Generally, costs may be covered:

• Fully or partially by private insurance, public insurance, or employer plans
• Under durable medical equipment (DME) benefits or sometimes under pharmacy benefits

Coverage decisions often consider:

• Type of diabetes
• Whether the person uses insulin, especially multiple daily injections or pump therapy
• History of severe lows or difficulty controlling glucose
• Documentation and prior authorization requested by the insurer

Without coverage, monthly costs can be significant. With coverage, users may pay:

• A monthly co-pay
• A percentage of device cost
• A deductible, after which coverage improves

Because specifics depend heavily on the individual plan and region, many people contact:

• Their insurance company
• Their clinic’s insurance coordinator
• The device manufacturer’s support line (for general guidance)

to get a clearer picture of expected costs before starting.

Practical Tips for Getting Started with a CGM

If you’re considering a CGM, there are some practical steps and questions that can help you prepare.

Questions to Discuss With a Healthcare Professional

You might explore topics such as:

• Is a CGM appropriate for my situation? Why or why not?
• What specific goals would we track with a CGM? (e.g., fewer lows, better overnight awareness, pattern discovery)
• Which general type of CGM system might fit my lifestyle? (wear location, calibration needs, phone compatibility, alerts)
• How often should I review my CGM data together with the clinical team?

Conversations like these can help ensure the device is used in a way that aligns with your individual health plan.

Everyday Use: What to Expect

People new to CGMs often report a short adjustment period. Common experiences include:

• Mild discomfort or awareness of the sensor for the first day or two
• Learning how to place sensors in less-bumped areas of the body
• Discovering which clothing or activities are more likely to dislodge the sensor
• Experimenting with alert settings to avoid constant alarms

Clear instructions are provided with each device, and many clinics offer additional training or educational resources.

Quick-Reference: Pros, Cons, and Cost Considerations of CGMs

Here’s a compact overview for easy review 👇

🌟 Main Advantages

• Continuous monitoring with frequent readings
• Trend information (up, down, stable)
• Customizable alerts for highs and lows
• Fewer routine fingersticks with certain systems
• Data history for pattern discovery and informed discussions with professionals
• Optional sharing with family or care teams

⚠️ Main Drawbacks

• Higher upfront and ongoing cost than traditional meters
• Insurance coverage may be limited or conditional
• Device wear can be uncomfortable or inconvenient for some
• Potential accuracy limitations, especially during rapid changes
• Risk of data overload or anxiety about numbers
• Occasional technical issues or sensor failures

💰 Cost and Access Tips

• Check insurance coverage carefully, including deductibles and co-pays
• Ask your clinical team if they can help with prior authorization
• Inquire about trial periods or sample programs, if available in your region
• Consider whether your existing phone or devices are compatible
• Factor in ongoing sensor replacements, not just the initial purchase

Making Sense of CGM Data Without Getting Overwhelmed

Once a CGM is in place, the question becomes: What do I do with all this information?

Many users and professionals focus on patterns rather than individual numbers, such as:

• Are lows happening frequently at similar times of day?
• Are levels consistently rising after certain meals or snacks?
• Are nighttime levels staying relatively stable or drifting up/down?

Some CGM platforms provide summaries like:

• Average glucose over a period
• Time spent within, above, or below a target range
• Daily reports or “glucose profiles”

Interpreting this data usefully often involves:

• Setting realistic, individualized goals
• Tracking long-term changes, not just single-day swings
• Using insights as conversation starters with healthcare professionals, not as self-judgments

When a CGM Might Not Be the Right Fit

While many people find CGMs helpful, they are not ideal for everyone. Situations where a CGM may be less suitable can include:

• Cost or coverage barriers that make long-term use unrealistic
• Individual preferences against wearing a device on the body
• Significant skin sensitivity or adhesive reactions
• Lack of consistent access to compatible phones or receivers
• Difficulty or discomfort with technology and apps, if support is limited

In these scenarios, traditional meters or periodic CGM use under professional supervision may be more practical, depending on individual needs and guidance.

Bringing It All Together

Continuous glucose monitors sit at the intersection of medical devices and everyday life. They offer something fingerstick meters cannot: a moving picture of glucose levels over time, rather than isolated snapshots. For many people managing diabetes—especially those on insulin—this ongoing flow of information can make daily decisions feel more informed and less like guesswork.

At the same time, CGMs come with clear trade-offs: higher costs, ongoing supplies, wearable hardware, and a constant stream of data that can be either empowering or overwhelming. They do not replace professional care, and they do not automatically improve health on their own. Their value depends on how they are used, interpreted, and integrated into a broader plan.

If you are curious about a CGM, the most practical next step is to have a focused conversation with a healthcare professional, asking about:

• Whether a CGM aligns with your medical situation
• What realistic benefits and limitations to expect
• How coverage and costs might look in your specific case

With clear expectations and guidance, a CGM can move from being a mysterious piece of technology to a useful tool—one more option in the growing world of medical devices designed to help people better understand and manage their health.