Do alarms work in airplane mode?

An alarm is a local timer. When you save one, the operating system records the time and wakes the device itself using the hardware clock that keeps running whether or not the screen is on. No server is involved at any point, which is why alarms have always worked on planes, in basements, on trains through tunnels, and on phones with no SIM in them at all.

This is worth being precise about, because it is the opposite of how most things on a phone now behave. Messages, weather, your calendar and almost every notification you receive arrive because something reached your device over a network. An alarm does not. It is one of the few remaining pieces of a smartphone that is entirely self-contained, and airplane mode does not touch it.

Turning airplane mode on disables the cellular radio, Wi-Fi and Bluetooth. None of those three is involved in scheduling an alarm, storing it, or firing it. The alarm was already written down locally the moment you tapped Save.

This is the distinction that catches people out, and it is the one genuine exception. Airplane mode leaves the phone running with its radios disabled. A powered-off phone is not running at all, and on both iPhone and Android a fully powered-off phone will not sound an alarm.

If you are flying and planning to sleep, the practical implication is simple: airplane mode is fine, powering the phone off is not. If you power down for takeoff, you have to remember to power back up before you sleep, and remembering to do something before you sleep is exactly the thing an alarm exists to compensate for.

A phone that runs out of battery is the same situation as a phone that was switched off. If the flight is long and you are relying on the alarm at the end of it, the charge level matters more than the connection does.

Alarms are stored as wall-clock time, not as a fixed point in absolute time. An alarm set for 7:00 means "when this phone believes it is 7:00". That is almost always what you want, and it is why an alarm keeps working sensibly when you travel. It also means the alarm moves when the phone updates its idea of what time zone it is in.

Both iPhone and Android update the time zone automatically, and both do it using the network and location services. In airplane mode, neither is available. A phone that has been in airplane mode since takeoff is still on the departure time zone when you land, and your 7:00 alarm will ring at 7:00 in the city you left.

1. 1If you need an alarm shortly after landing, take airplane mode off as soon as you are allowed to and give the phone a minute to find a network. The time zone updates on its own once it does.
2. 2If you would rather not wait, set the time zone manually. On iPhone that is Settings, then General, then Date & Time; on Android it is under Settings, then System, then Date & time. Turn off the automatic option and choose the destination.
3. 3Check the alarm afterwards. Changing the time zone does not change the time you typed, so confirm the alarm still reads the hour you actually want.

The guarantee above belongs to the operating system, not to any particular app. A third-party alarm app can undo it, and some do. There are three patterns worth checking for before you rely on one somewhere without signal.

• Advertising shown on the ring or dismiss screen. If the advert has to load before you can silence the alarm, no network means a stuck screen and an alarm you cannot turn off.
• Cloud features on the dismiss path: a puzzle generated on a server, a photo uploaded somewhere to be matched, or an account check that has to succeed before the app will let you through.
• Sounds streamed rather than bundled, including music-service integrations. If the alarm tone lives on a server, an offline phone has nothing to play.

None of these is exotic. Each one is a normal product decision that happens to put a network request on the one path that must never need one, and none of them is visible from a store listing. The failure only shows up on the morning you are somewhere with no signal, which is the morning you were relying on it.

Roosta treats this as a hard rule rather than a feature: nothing on the alarm path requires a network. Alarms are registered with the operating system, all 21 sounds ship inside the app rather than being streamed, and camera missions run their recognition on the device. A phone in airplane mode still wakes you up, and every mission still works.

Any alarm app can claim it works offline. Checking takes two minutes and is worth doing once, before a trip rather than during one.

1. 1Turn airplane mode on, and turn Wi-Fi off as well if it stayed enabled.
2. 2Set an alarm for two minutes from now.
3. 3Lock the phone and put it face down. Testing with the screen on and the app open hides exactly the failures you are looking for.
4. 4When it rings, dismiss it completely. The ring is only half the test; an app that rings but cannot be dismissed without a connection has still failed.

If it rings and dismisses cleanly with the radios off, it will behave the same way at altitude, in a hotel with broken Wi-Fi, or on a phone whose data ran out.