Lemon-squeezy.
Ok, I have $200 burning here to pay you such a device. Can you make it installable outside? Under a roof, but still subject to temperature-changes? No? Ok, I'll set it up inside.
May need more than 10 hours, but doable within a day or so.
Sure. Take a week. But, if it does not work by then, you pay me back $300. Deal?
Wireshark for WiFi Sniffing and logging
Oops... I'm afraid, you didn't quite get it. I don't want to listen peer with their transmitters. I just want to log their appearing. My own side should be as passive as possible — to conceal my own capabilities.