To get a glucose alarm that works in silent mode on iPhone, you need alerts that are allowed to ignore the ringer switch, Do Not Disturb and every Focus mode. On iOS this means using an app with Critical Alerts turned on, or setting your CGM notifications to bypass silencing and Focus. Once configured correctly, your low and high glucose alarms will play a loud sound and light up the screen even when the phone is muted or your family is asleep.
The short version: A standard notification will not sound when your iPhone is silenced or in a Focus mode, so a low glucose alert can go unheard. Enabling Critical Alerts (or allowing time-sensitive alerts through Focus) lets your CGM alarm break through and sound at full volume.
Why glucose alarms go silent on iPhone
By design, iPhone tries to keep quiet when you tell it to. The physical ring/silent switch, Do Not Disturb, Sleep Focus and Driving Focus all mute most notifications. That is great for meetings and movies, but it is a real problem when a low blood sugar alarm needs to wake you at 3 a.m.
Apple created a special notification category called Critical Alerts for exactly this situation. Critical Alerts can play a sound and vibrate even when the phone is muted or in any Focus mode, and they can override the volume setting. Health and safety apps must request permission from Apple to use them, and you must turn the permission on.
If you rely on real-time CGM data, understanding this is essential. You can read more about why these alerts matter in our guide on why real-time glucose alerts matter.
How to make CGM alerts work through silent and Do Not Disturb
The exact steps depend on which app is delivering your alarms, but the settings live in the same places on every iPhone.
1. Turn on Critical Alerts for your CGM or companion app
- Open Settings, then Notifications.
- Tap the app that sends your glucose alerts.
- Turn on Allow Notifications, then enable Critical Alerts if the app offers it.
- Make sure Sounds is on and pick a distinct alert tone.
Critical Alerts is the single most important switch. When it is on, the alarm plays even if your ringer is off and Sleep Focus is running.
2. Allow the app through your Focus modes
- Open Settings, then Focus.
- Choose each Focus you use, such as Do Not Disturb, Sleep and Driving.
- Under Allowed Notifications or Apps, add your CGM app so its alerts are never held back.
- Turn on Time Sensitive notifications for the app if you see that option.
3. Check volume and Attention Aware settings
- Raise your ringer and alerts volume in Settings, Sounds & Haptics.
- On Face ID iPhones, Attention Aware Features can lower alert volume when you look at the screen. If you want alarms to stay loud, you can turn this off in Settings, Face ID & Passcode.
- Test with your phone muted. Trigger a test alert if your app allows it, or wait for a real high or low, and confirm you hear it.
Do all glucose apps support Critical Alerts?
Not automatically. Some apps default to standard notifications, which the phone can silence. Others offer Critical Alerts but leave them off until you switch them on. After any iOS update or app reinstall, it is worth checking your notification settings again, because permissions sometimes reset.
Manufacturer apps for FreeStyle Libre and Dexcom include their own alarm systems, and those alarms are your primary safety net. A companion app can add a second layer of alerting on your iPhone and Apple Watch, but it should never replace the alarms built into your CGM device and its official app.
How Sugar Sense handles silent mode
Sugar Sense is built to alert you clearly. When you enable Critical Alerts, your high, low and predictive heading-low warnings can sound at full volume even in silent mode or a Focus. You can also see your latest reading on your Apple Watch and iPhone at a glance, so a quiet phone in your pocket is never the only thing standing between you and a low.
Nighttime lows: why silent-mode alarms matter most
Many people set their phone to silent or Sleep Focus overnight, which is exactly when a falling glucose can be most dangerous and hardest to feel. This is why a working overnight alarm is so important.
A helpful safety feature is a predictive low alert, which warns you that glucose is heading down before you actually cross your low threshold. That extra lead time can be the difference between a small snack and a serious event. Learning to read glucose trend arrows helps you understand these warnings faster.
If overnight lows worry you, do not rely on hearing a single quiet buzz. Combine Critical Alerts, a loud tone, and if you have a caregiver, remote monitoring so someone else gets alerted too. Our caregiver’s guide to remote glucose monitoring covers how family members can follow readings and receive their own alarms.
Troubleshooting: my glucose alarm still is not sounding
- Critical Alerts is off. Recheck Settings, Notifications, then your app. This is the most common cause.
- The app was removed from a Focus. Re-add it to Sleep, Driving and Do Not Disturb.
- Volume is at zero. Ringer volume and Critical Alert volume can be separate. Turn both up.
- No data is arriving. An alarm cannot fire without readings. If your feed has stalled, see our FreeStyle Libre troubleshooting or Dexcom troubleshooting guides.
- Bluetooth or internet dropped. Apps that pull from LibreLinkUp, Dexcom Share or Nightscout need a connection. Reconnect Wi-Fi or cellular.
- Low Power Mode. This can delay background updates. Keep your phone charged overnight.
Frequently asked questions
Will Critical Alerts drain my battery?
No more than normal notifications. Critical Alerts only change how loudly and when an alert plays, not how often your app checks glucose. Keeping your phone charged overnight is still a good habit for reliable alarms.
Can a glucose alarm override the physical silent switch?
Yes, if it is delivered as a Critical Alert. That is the whole point of the category. Standard and time-sensitive notifications cannot override the ring/silent switch, but Critical Alerts can.
Does silent mode affect my Apple Watch glucose alerts?
Your Watch has its own silent mode and haptic settings. Check that Critical Alerts are allowed on the Watch too, and consider leaving haptics on so a strong tap on your wrist backs up the sound. See our guide to CGM on Apple Watch for setup tips.
Should I turn off my CGM device alarms if my phone alerts me?
No. Keep the alarms in your official CGM app on. A companion app is an extra layer, not a replacement. Treatment thresholds and alarm settings should be discussed with your healthcare team.
Sugar Sense is a free companion app that shows real-time readings from FreeStyle Libre, Dexcom and Nightscout, with high, low and predictive heading-low alerts that can use Critical Alerts to sound in silent mode and through Focus. If you want dependable alarms on your iPhone and Apple Watch plus family sharing, see how Sugar Sense keeps you and your Care Circle in the loop.
This article is for education and general information only. A companion app never replaces your CGM device, its official app or its built-in alarms, and no phone setting is a guarantee. Always confirm alerts are working, and make all treatment decisions with your healthcare provider. See our medical disclaimer.
