A bus stop alarm has to be set differently to a train alarm

The spacing problem

City bus stops are commonly 200 to 400 m apart. That single fact undoes the advice that works for rail. On a route with 300 m spacing, a 1 km trigger radius — modest on an intercity train — puts the trigger point roughly three stops back, so that is where the alarm will tend to fire. An alarm that is predictably wrong by three stops is one you will start ignoring, which is worse than not having it.

So on a bus, start at the bottom of the range. Nap Alarm goes down to 200 m, and on a dense urban route that is often the right setting, or close to it. The rule from the GPS alarm page applies with more force here: your buffer must be smaller than the gap between your stop and the one before it.

Why ETA mode often suits buses better

A small radius solves the spacing problem and creates a new one. On a road, the time it takes to cover the last 300 m is not a fixed quantity — it depends on the lights, the traffic, and how many people are boarding ahead of you. It might be forty seconds. It might be four minutes.

This is what time-based mode is for. Instead of a fixed radius, you set a number of minutes, and the app recalculates your projected arrival as conditions change. You get a consistent amount of warning rather than a consistent distance. On a bus, consistent warning is the thing you actually want.

Distance mode still wins where traffic is not the variable — an express or orbital route with long gaps between stops behaves more like a train, and a fixed radius is simpler and more predictable there.

Request stops change the maths

On a lot of routes the bus will not stop unless somebody rings. If that applies to yours, the alarm is not there to wake you as you arrive — it is there to wake you early enough to press the bell and be believed.

Practically, that means adding the bell to your buffer. Give yourself the stop before: enough warning to sit up, work out where you are, ring, and get to the door while the driver still has room to pull in. It is the one case where erring wide is clearly right, even on a route with close stops.

GPS accuracy in a built-up area

Bus routes run through exactly the environment consumer GPS handles worst. Between tall buildings, satellite signals reach your phone after bouncing off surfaces, and the reported position wanders — often by more than the distance between two stops.

You cannot fix this from an app, so plan around it: a buffer of a few hundred metres absorbs the wander, while a very tight one will sometimes fire late or in the wrong place. This is the main reason not to set the smallest possible radius just because the stops are close.

Setting one before your commute

1. Search for the stop, or save it as Home or Work if it is the same one every day — a saved location makes it a one-tap setup.
2. Decide between distance and ETA mode using the route: dense and traffic-bound suggests ETA, long gaps between stops suggests distance.
3. Set the buffer against the actual gap between your stop and the previous one, and add margin if you have to ring the bell.
4. Connect headphones if you would rather not wake the bus, then lock the phone.

If you forget to arm it, the geofence reminder can prompt you as you leave a saved location like the office, before you board.

Honest limitations

• On very closely spaced stops, no trigger distance separates your stop cleanly from its neighbour. The alarm gets you to roughly the right place — the last stop or two is on you.
• Diversions take you off the route you saved. The alarm still watches your distance to the destination, but a diverted bus may approach from an unexpected direction and trigger differently to usual.
• Underground sections are rare on bus routes, but if yours uses a tunnel, the behaviour is the same as on the metro: predicted position rather than measured.