# Vehicle buttocks detection

In my truck a warning light comes on when I go to take off if a passenger is sitting there but the seatbelt is not secured. After some research and thinking it may be their weight, capacitance or maybe an infrared beam (although I cannot see a sign of that). Maybe other things I haven't thought of?

I am a furniture manufacturer and would like to incorporate a night light into furniture to have a light come on at night automatically when someone stands up. The truck gave me the idea and I was thinking because they sell so many they have probably put a lot of thought into how they work. Does anyone know the solution the auto industry uses or have other good ideas on ways to go about it?

• Since the actual problem is about how to detect whether a person is sitting down or not, the specific mechanism used in a vehicle may not be relevant. A suggestion: Sensing load is probably easiest at a DIY level, so why not just run with that? – Anindo Ghosh May 25 '13 at 10:10
• For seats with sufficiently thick padding: magnet and reed switch separated by foam, brought into proximity by its compression. – Kaz May 25 '13 at 15:58

you can use FSR(force sensitive resistor) to detect whether a person is sitting on a seat or stands up. The working of FSR is similar to LDR (Light dependent resistor the resistance of LDR would decrease if light falls much),in FSR if the applied pressure/weight increased the the resistance would get decreased,you can calibrate this resistance change in terms of weight/pressure.

fig(1) weight Vs Resistance and conductance

fig(2) circuit diagram- connection of FSR

fig(3) Output voltage Vs wight(response of circuit diagram fig(2))

 For more details http://www.tekscan.com/flexiforce/force-sensors-for-design