GPS alarm vs a normal alarm
Both wake you up. They disagree about what should decide when. A clock alarm fires at a time you guessed before you set off; a location alarm fires when you get somewhere. On a journey whose timing you can't predict, that is the whole argument.
Where the clock alarm breaks
Setting a time alarm for a commute means committing, before you leave, to a prediction: this journey will take thirty-four minutes. You are not usually wrong by much. But public transport doesn't fail gracefully around that estimate — it fails in both directions, and both are bad.
Running late means the alarm goes off while you are still two stops out. You look up, see you are not there, and go back to sleep — and the alarm has now fired, so nothing else is coming. The early failure is the one that actually costs people their stop, and it is the one nobody plans for.
Running early — the service skips a scheduled call, or the traffic simply clears — means the alarm fires after you have gone past. By the time you are awake you are working out how far back you have to come.
What the location alarm changes
A GPS alarm removes the guess. You don't tell it how long the journey will take, because it doesn't need to know. It watches the distance between you and the destination, and fires when that gap closes to the size you chose. A delay makes the journey longer; it does not make the destination move.
The cost is that it needs to know where you are, continuously, for as long as you are travelling. That means a location permission that works in the background and a real, if modest, battery draw. Those are the terms of the trade — there is no version of this that watches your position without watching your position.
Side by side
| Normal alarm | GPS alarm | |
|---|---|---|
| What it measures | Clock time you set in advance | Distance between you and a destination |
| If the service runs late | Fires early, while you're still short of your stop | Unaffected — the distance is what it is |
| If the service runs early | Fires after you've passed your stop | Unaffected |
| Setup effort | Guess the journey time | Pick a destination and a trigger distance |
| Permissions needed | None | Location, including while the app is in the background |
| Battery cost | Negligible | Real — position is tracked for the whole journey |
| Works with no signal | Yes | Needs a satellite fix, or a prediction to stand in for one |
The hybrid: waking by projected arrival
There is a third option that sits between the two, and on some journeys it beats both. Time-based mode on Nap Alarm sets the alarm for a number of minutes before arrival, but keeps recalculating when that arrival will be as traffic and delays change.
You get the thing a clock alarm was supposed to give you — a consistent amount of warning — without having to predict the journey yourself. On a road route where the last kilometre might take two minutes or ten, this is usually the better setting. The bus stop alarm page goes into when to reach for it.
When a normal alarm is still the right answer
Not every case calls for location tracking, and pretending otherwise would be dishonest:
- Your journey genuinely doesn't vary.A short, reliable hop you have timed many times doesn't need GPS. A clock alarm is simpler and costs no permissions.
- You would rather not grant background location. A completely reasonable position. A location alarm cannot work without it, so a clock alarm is the honest alternative.
- Your battery is nearly flat. On 5% at the start of a long trip, continuous tracking is the wrong thing to spend it on.
- You are not actually going to sleep. If you are awake and watching the stops, an alarm of either kind is unnecessary.
Everywhere else — which on public transport is most journeys — the location alarm is measuring the thing that actually determines whether you make your stop. How to set one up is covered on the GPS alarm page.