Are you a Boston subway regular? Wondering if you have time to finish drinking that coffee or reading that article? Running down the station stairs because you thought you heard a train arriving? Now you’ll know.

The MBTA Realtime T app tracks Boston’s MBTA subway trains in real time, accurately predicting when each train will arrive at your station. The app shows the location of each train on the line, as well as the estimated arrival time, down to the second, at each station. It works using sensors placed on the tracks–when a passing train triggers a sensor, MBTA Realtime T app is the first to know.

The app supports the Red, Orange, and Blue heavy rail lines. The Green Line is not supported, as the MBTA has not yet installed tracking technology on the Green Line.