You might want to look into "hardware watchdogs". The Raspberry Pi includes an internal
A hardware watchdog reboots the whole system by force unless it is recieves an "i'm alive" signal from software running on the Pi regularly. If the software hangs (perhaps a kiosk app or Linux itself), the signal does not get sent, a timer starts ticking and after 2, 10, 15 or whatever seconds the Pi is forcefully resetted.
If you want an external watchdog instead of the internal one, you would need both a timer component and a relay. The relay would cut and reinstate power to the Pi (reboot it). A relay is an electromechanical switch which is controlled by electricity. You can use a relay to turn off/turn on devices with big elctricity requirements with small control currents/voltages.
Fun fact : This sounds similiar to a laymans explanation of a transistor , doesn't it ? Relays were indeed used to build the first computers before transistors were invented.
• Don't like the board ? Missing features ? Change to the prosilver theme ! You can find it in your settings.
• Don't like to search the forum BEFORE posting 'cos it's useless ? Try googling : yoursearchtermshere site:raspberrypi.org