After vandalism (two cars tires slashed, cool-aid in pool) at the house I want to create some type of monitor that would alert me inside the house that someone or something has passed within the alley behind my home. The alley is about 50' from the house. I don't think I am going to be able to use something that crosses the alley as the back side neighbor might not want something on his fence.
I want the circuit to monitor traffic and emit a flash and short beep inside the house. I would turn the circuit on at night. Any tips, recommendations?