The whole central on your phone. It opens this central and nothing else, over an encrypted connection it checks itself, and you sign in every time you open it.

Download for Android

Installing it

1. Tap Download, then open the file when it is done.
2. Android asks once to allow installing apps from your browser — allow it, go back and tap Install.
3. Open SIMP Central and sign in with your central account.

Only accounts the owner switched the app on for can sign in from it (Settings → Users & rights → Phone app). A newer version is offered inside the app by itself.

iPhone

Open central.speed-in-motion.be in Safari, tap Share → Add to Home Screen. It opens full screen like an app.