CGM Alerts and Alarms: How to Set Them Properly

Why CGM Alerts and Alarms Matter

Continuous Glucose Monitors (CGMs) are among the most powerful tools available for diabetes management — but only when configured correctly. The alerts and alarms built into systems like the Dexcom G7, Freestyle Libre 3, and Medtronic Guardian are designed to notify you before dangerous highs or lows occur. Set them too loosely, and you miss critical warnings. Set them too tightly, and alarm fatigue sets in, causing you to ignore the very alerts meant to keep you safe.

Getting your CGM alert settings right is a balance of personalization, clinical guidance, and lifestyle awareness. This guide will help you understand each type of alert, how to set meaningful thresholds, and how to fine-tune your system over time.

Understanding the Types of CGM Alerts

High Glucose Alerts

A high glucose alert notifies you when your blood sugar rises above a set threshold. Most systems allow you to choose the level at which the alert fires. For many adults, a common starting point is 180–200 mg/dL, though your endocrinologist may recommend tighter or looser targets depending on your history of hypoglycemia unawareness, A1C goals, and daily routine.

Low Glucose Alerts

Low alerts are among the most critical safety features of any CGM. The standard recommendation from the American Diabetes Association is to alert at 70 mg/dL — the clinical threshold for hypoglycemia. If you have hypoglycemia unawareness or drive frequently, setting the low alert at 80 mg/dL gives you additional reaction time.

Urgent Low Alerts

Most CGM systems include a separate urgent low alarm — typically fixed at 55 mg/dL — that cannot be disabled. This alarm uses a distinct sound pattern to indicate a potentially dangerous situation requiring immediate action.

Rate-of-Change Alerts

These alerts notify you not just of where your glucose is, but how fast it's moving. A rapid drop alert (e.g., falling more than 2–3 mg/dL per minute) gives you advance warning before you actually become hypoglycemic. This is especially valuable overnight or during exercise.

Signal Loss and Sensor Alerts

When your CGM sensor loses connection or approaches the end of its wear period, you'll receive a signal loss or sensor expiration alert. Keeping a backup supply of CGM sensors ensures you're never left without coverage. MDS Diabetes carries a wide selection of CGM sensors and supplies at mdsdiabetes.com, so you can stock up easily without interruption.

How to Set Your Alerts Properly

• Start with clinical defaults: Use your device's default settings as a baseline before customizing.
• Consult your care team: Your endocrinologist or diabetes educator can recommend thresholds aligned with your A1C targets and hypoglycemia risk.
• Adjust for lifestyle: Set a lower high alert threshold on active days, or a higher low alert if you exercise in the morning.
• Use snooze features wisely: Most systems allow you to snooze repeated alerts. Don't snooze low alerts — only snooze highs after you've taken corrective action.
• Enable caregiver sharing alerts: Systems like Dexcom Follow allow a parent, spouse, or caregiver to receive your alerts remotely — a critical safety net, especially overnight.

Avoiding Alarm Fatigue

Alarm fatigue happens when too many notifications cause you to tune them out entirely. To prevent this, limit your active alerts to the ones that truly require action. Avoid setting high alerts at 140 mg/dL if your post-meal glucose routinely reaches 160 mg/dL — you'll receive constant alerts that erode trust in the system. Instead, work with your care team to set realistic, meaningful thresholds that alert you to genuine outliers.

Keeping Your CGM System Stocked and Ready

No alert system works without a functioning sensor. CGM sensors have a limited wear period — typically 10 to 15 days depending on the device — and should be replaced on schedule to ensure alert accuracy. Sensors that are past their wear window may give inaccurate readings, causing false alerts or missing real events. Shop for replacement CGM sensors, transmitters, and accessories at mdsdiabetes.com to keep your system running without gaps.