four-channel GPS receiver using a repurposed FPGA board from a previous frequency synthesizer project. Connected to a PC running a console app, the receiver is capable of tracking four satellites simultaneously, which is good enough to capture lat, long, and altitude.
basically the Flash Nap project with a few extra features and some work. It's also a minimal version of "Light/Sound" hypnosis machines that cost hundreds of dollars, but if you have parts, this one will cost just a couple of bucks. NO PROGRAMMING REQUIRE
Nice little guide to building an IR transceiver - uses the USB port for stable 5V, but includes a link in the comments to a decent circuit diagram that uses a voltage regulator and therefore doesn't need the USB port for power.
a small device which plugs into a $20 prepaid mobile phone to make a GPS tracker. The Tracker responds to text message commands, detects motion, and sends you its exact position, ready for Google Maps or your mapping software
2.4GHz parabolic mesh dishes from Chinese cookware scoops & a USB WiFi adaptor! Called "WIFRY","WOKFI" or "WOKTENNA" (12"= 300mm diam) shows 12-15dB gain (enough for a LOS range extension to 3-5km)
A remote control car that can be driven over the internet or with a laptop wirelessly from up to 500m away. It has a live-feed network camera so that it can be driven without line of sight and a horn so that you can honk at people.