A docco on BNFL said that alarms in the swimming pool storage areas ping continuously at low background rate so you know the alarm is receiving voltage, and basically works. It doesn't mean it can't fail but as an electromechanical liveness/heartbeat check it made a lot of sense.
I believe even fly by wire cockpits have some direct mesurement sensors, a pitot tube is about as simple as it comes. Not infallible either (wasps, ground covers not removed...)
I believe even fly by wire cockpits have some direct mesurement sensors, a pitot tube is about as simple as it comes. Not infallible either (wasps, ground covers not removed...)