Traveling by bus has one advantage that metro and train riders don't get: a clear view of the sky for the entire trip. An alarm to not miss your metro station has to deal with one extra variable: underground stretches, where the GPS momentarily loses its lock on the satellites. The good news is that this has a simple solution, and that is exactly what this guide covers: how the signal behaves inside the tunnel, which radius to set for each type of line, and why this approach still beats counting stations in your head by a mile.
What happens to the GPS inside the metro tunnel
Inside an enclosed tunnel, surrounded by earth and concrete, the GPS satellite signal weakens and can even disappear for a few seconds. This is not a flaw in the app, but a physical limitation of GPS itself, which depends on a line of sight to the sky. Any location alarm, in any app, runs into the same limitation inside a tunnel.
What changes is how the app handles that fluctuation. Don't Miss The Stop keeps running in the background and uses whatever signal is available (including weaker or partial signals) to maintain an estimate of your position. As soon as the train leaves the tunnel or the car passes through an open station, the GPS picks up a clean signal again, the app recalculates your position immediately, and the alarm goes off normally if you are already within the radius you set.
Even with a few seconds of fluctuation in the tunnel, the app adjusts as soon as the signal returns. What changes is how close to the radius you will already be when that happens. That is why the radius matters more on underground lines than on surface routes.
It's worth stressing that this has nothing to do with internet or mobile data: GPS is a satellite signal, so the lack of cell coverage inside the tunnel doesn't affect the alarm. The same principle is detailed in the offline location alarm guide, about how the app works in areas with no connection at all.
Metro, train, and light rail: not every line has the same signal
Not every rail line runs through the same type of route, and that changes the reliability of the GPS signal along the way quite a bit:
- Underground metro: entire stretches below ground, with open stations in between. This is where signal fluctuations are most frequent, though brief.
- Regional and commuter train: tends to alternate between surface stretches, elevated sections, and some shorter tunnels. Exposure to an open signal is greater than on the metro, but blind spots still exist.
- Light rail: runs mostly on surface tracks, often down the middle of the street, with an almost constant view of the sky. This is the most stable scenario for GPS.
Another common trap on unfamiliar lines: similar station names, announcements muffled by the noise of the car or drowned out by your headphones, and a station count that easily gets scrambled after the fifth or sixth stop. A location alarm ignores all of that: it doesn't count stations, it just watches the real distance to the point you marked on the map. To understand this principle, see What a location alarm is.
Which radius to set: underground vs. surface lines
Since the signal behaves differently between an underground metro station and a surface train station, the radius setting should also follow the type of line:
- Mostly underground metro: use a radius between 500 m and 1 km. That extra margin makes up for the seconds when the app goes without a GPS update inside the tunnel, giving it enough time to recalculate when the signal returns.
- Regional train with surface stretches: a slightly smaller radius, between 300 m and 700 m, usually works well, since exposure to an open signal is greater.
- Light rail or surface trains: a smaller radius, starting at 200 to 300 m, is usually enough. The signal stays stable from the start to the end of the trip.
When in doubt, err toward a larger radius. A few extra meters of warning cost you little (at most you wake up a little earlier), while a radius that's too small on an unstable line can mean waking up already past your station.
How to set up an alarm to not miss your metro station
The setup is the same on any line: all that changes is the radius and, if you want, the type of alert. Here is the step by step:
Tap the exact spot or search for the station name. If the line has similar names, check on the map that the pin landed on the right spot before moving on.
Use something between 500 m and 1 km on underground stretches, or a smaller radius on surface trains and light rail, as covered in the section above.
Vibration only mode is handy in a crowded, quiet car; headphones only mode avoids bothering the people around you.
You can lock the screen with no problem: the app keeps monitoring in the background until you get close to the station.
Why an alarm is more reliable than counting stations
Counting stations in your head seems simple until you doze off, turn up your headphones, or take a line you don't ride every day. Any one of those is enough to lose count. And unlike the bus, where you can glance out at the street and recognize the neighborhood, underground almost every station has the same lighting and the same kind of signage.
A location alarm solves this directly, and the app also covers specific needs for people who rely on the metro or train every day: you can save as many favorite stations as you like, keep more than one alarm active at the same time (handy on transfers, with one alarm at the transfer station and another at the final destination), and schedule a favorite to arm itself on fixed days and times, like the Monday to Friday commute to work. Having multiple favorite destinations saved is what makes this kind of routine practical, without reconfiguring anything every day.
Today the app has a 4.7 rating across more than 1,400 reviews and over 50,000 installs. The free version already covers the essentials; Premium exists for anyone who wants unlimited simultaneous alarms, automatic scheduling by day of the week, dark theme, and no ads.
Frequently asked questions
Does the alarm work inside the metro or in tunnels with no GPS signal?
On underground stretches the GPS can lose its signal for a moment. As soon as the train returns to the surface or passes through an open station, the app recalculates your position and triggers the alarm normally.
What is the ideal radius for an alarm on underground metro lines?
For fully underground stretches, we recommend a radius between 500 meters and 1 km, which gives a comfortable margin for the app to recalculate your position as soon as the GPS signal comes back. On surface trains or light rail, with a clear view of the sky, a smaller radius usually works well.
What is the difference in GPS signal between the metro and light rail?
Light rail runs mostly on the surface, on open tracks, so the GPS signal tends to stay stable from the start to the end of the trip. The metro, on the other hand, alternates between underground stretches and open stations, so brief signal fluctuations inside the tunnels are more common.