water balloon hanging over doorframe

Laser triggered waterbomb trap

Back at school I built a little trap in order to fool some other pupils.
At first I took apart an old CD-drive and removed the laser-moving unit:
the laser unit
The laser unit will be used as our trigger mechanism.
Just solder a connection to the motor and add a needle to the moving part.
The needle will move forward and pop our waterballoon.
I used a laser and a photocell to build a lightbarrier which would activat the trap.
The light barrier was placed across the pupils’ common room.
Here’s the trap’s schematic:
This is the laser and the receiver (both are battery powered) :
receiver with relais
If the laser beam is interrupted the relais will activate the CD-drive-trigger and pop the waterbomb right over somebody’s head.
Here the mounted trigger armed with one waterbomb:
And here the first victim (of course with slowmow) :
So this is one way to have fun with your old CD-Drive!


  1. This is absolutely brilliant. I wonder if you could do this on a larger scale, and set it up for a cup of water? A Bucket??


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