The variety of traps that can be created is as infinite as the creativity of those who make them. This category instead is a listing of existing game effects that can be triggered when a trap goes off.
The most common type of trap is a single step mechanism, which is a prop with some kind of tripwire type activator and a noisemaker. Trigger the noisemaker and you spring the traps effect, which should be noted somewhere on the trap. Trap effects are automatically assumed to hit the torso. When the trap goes off the effect inside is immediately consumed.
When a noisemaker goes off players should make a good inspection of the item for trap information before assuming the trap was simply a noisemaker. If the trap is not loaded with a specific effect it is an "alarm trap". Only someone with the tinkerer skill may set or disarm a trap.
When building a single-step mechanism your aesthetic goal here: to be discrete. You can use modern electronics; it would be near impossible to do it otherwise. But, it is optimal to hide these as much as possible.
What your looking for is a piezo buzzer. The Props and Atmosphere Marshal prefers the ones that can run off a single double A. The ones he uses have a Voltage range and can function safely on several battery types. A 9V is as loud as a fire alarm, going down to a single double A keeps it loud enough that it is known/won't be missed, but not "HEY EVERYONE ON SITE! I SET OFF A TRAP!"
Contraptions are like single step mechanisms but designed to be more portable.