Help- Radar "tripwire" to connect to computer

Hi! I'm trying to make a "tripwire" of sorts that can connect wirelessly to my computer, alerting me when someone is coming. How would I go about doing that? I've seen laser pointer options, but I want a singular device so I thought radar or IR would be a better option. Any ideas?

out of stock but these work very well

hint use an interrupt to trigger your alarm.

hi, what you mean with "singular device"?

you can use a IRLED with IR Phototransistor or photoresistor to active the trigger and send a signal with some rf module

using a MCU or a encoder/decoder like a Door security sensor but with IR