A few tools have become standard kit for solo travelers. Start with what your phone already has: both major smartphone platforms include an emergency SOS function that calls local emergency services and can alert chosen contacts with your location; set it up and test how it triggers before departure.
Useful additions: your government's official travel app, where one exists, which pushes alerts for your destination and connects to consular help; your travel insurer's app with the 24-hour assistance line saved; offline maps of each city so navigation survives dead zones; and a translation app with the local language downloaded offline, which doubles as an emergency communication tool.
Low-tech redundancy still matters: emergency numbers written on paper, a photocopy of your passport separate from the original, and a charged power bank. And agree a simple check-in rhythm with someone at home, a daily message at whatever hour suits, so silence itself becomes the alarm. The best safety tool remains the one you have set up before you need it.