It can operate completely mechanically. There is an integrated UPS in case mains fails. If the battery also fails, a pneumatic whistle goes off to alert the user. If for some reason something goes really bad, they switch to using an ambu bag, typically hung on the back of the machine.
I like the idea of the pneumatic whistle. A pressure vessel with a sprung loaded valve held closed by a solenoid, maybe? However it works, it's a really neat piece of lateral thinking.
