Watchdog
I needed to make a friendly-looking "watchdog": something that would make it clear that an area was being watched while not being scary at all. The Gromit from this marvellous pair was absolutely ideal: add stepper motors, a small amount of electronics, some software and hey presto.
https://www.meades.org/misc/watchdog/watchdog.html
Printing instructions, software, etc. can be found at the link above.