I came across this little gem while I was patent-diving for a steam-engine valve. It’s an old-timey “portable burglar alarm” with a novel alarm system. It’s quite simple, but could be surprisingly effective at preventing illegal entry (or inducing sudden heart attack).

The alarm unit is hung from a peg above a door, through which the burglar would presumably enter. When the door is opened, it pushes the unit off the peg, and said unit plummets to the floor. When it hits the floor, the plunger “D” is pushed up into the housing, and firing pin “d” (lowercase) impinges on cartridge “c”, which fires, thus sounding an alarm.

It also makes provision in tube “e’ ” for storage of extra cartridges, a removable cartridge holder “B”, and a window through which the cartridge might be changed “a”.

The perfect way to prevent handlebar-moustachioed rapscallions from making illicit entry to your estates.