I can beat 8 seconds
My office is next to a small meeting room. If I lean to my left I can see through the door into it.
In it is a TV for projecting. Like most modern TVs it doesn't have an ON/OFF switch, but the TV is wired to a socket with a light on.
If TV is working - it's displaying something.
If TV isn't, then it's in standby and the standby light is on.
If there's no light - the power is off at the wall socket.
So, cue countless users reporting "the TV isn't working"
I lean, see the standby button isn't lit and the socket is switched off. Time - about 4 seconds.