I made this police car with only one wheel and combine a switch and a pressure sensor with paper based circuit.

For the switch sensor, I use a battery as one wheel, when I put any 3 round shape metal, for example: coins

as wheels on the car , the circuit will be connected, then trigger the 2 green head light.

For the pressure sensor, I made it and the switch sensor parallel connected, so when the four wheels are put

on the car, then I can use the pressure sensor to control the fade in/out of the red  alarm siren.

Paper Based Circuits with Switch

Paper Based Circuits with Pressure Sensor