Need some kind of easy to make/buy sensor

I have a small project that alerts when a condition is about 3V (high) and off when 1-2V (low). The only thing I'm missing now is some kind of sensor that can give me those conditions. Doesn't really matter what it is just aslong as it's easy to make or buy. Maybe something like a heat, water, motion....

Please feed me some ideas and maybe where I can get the info for it. Thank you.

buy a CDS cell. Its a light-dependent resistor.

now you need one more resistor.

connect the CDS and resistor in series. the connection point goes to your input.

Now you have a voltage divider.

Use the following equation:

R2 / (R1 + R2) * V

where R2 is the resistor between input and ground, and R1 is the resistor between input and VCC, and V is the supply voltage.

you might have to swap the resistor and CDS cell several times in order to get the best results.

and you can replace the resistor with a potentiometer.

2 small sheets of aluminium foil as a pressure mat, in series with a button cell when stepped on complete the circuit and provide a button cell voltage to your circuit . Put a resistor to ground on the output of the mat, so its voltage is at zero when not being stepped on, voila

Megamox