Rat traps must be checked frequently for disposal but are often hidden out of sight in the attic. I realized I could make a simple normally closed single pole single throw switch by soldering wires to the trigger bar and the moving bar of the trap. For this project I used lead-free solder. Ironically.
When the trap is set, the trigger bar holds down the moving bar, completing the circuit and lighting an LED in the garage. When the trap triggers, the LED goes out, and I'll know I need to check a trap.