You had better ring the bell before coming into my room, or maybe even my den? 

This fabulous DIY kit from Koa Koa will allow you to build your very own doorbell for the door to your room, engaging in STEAM learning (Science, Technology, Engineering, Arts & Mathematics)

Not only will they have a fun building it but they'll love playing with it afterwards.

How it works ?
Start by detaching the gears of wooden planks, then identify all the small parts and hardware. Once mounted, you can paint it to customize it and nail it at the door of your room (there are 4 holes on the sides for that purpose). 

What will you learn?
- The different types of gears: gear trains, rack, pinion, circular, etc.
- the ratios to calculate the speed at which the gears are turning
- the effect of friction, the crank