It's designed to call out gropers loud and clear and on the spot.
Cops in Tokyo came up with the "Digi Police" app and now it's said to be popular with women who are using it to protect themselves from molesters on packed rush hour trains.
If someone is being harassed they can press an icon and a message plays out loud saying: "There is a groper here. Please help." Another message repeatedly says, "Please stop!"
Police say this helps call attention to a problem on the spot and also helps people who are too afraid to call out for help.