| I once recovered a stolen car with ping. It was 2002 (2003?), and we had just launched Zipcar in New York. Being a naive start-up we had perhaps not the most stringent security measures in place to prevent fraud and theft. Sure enough, a couple of weeks in and one of our cars went missing. Calls to the member went unreturned, and it became clear that the member was not who they claimed to be and had no intention of returning the car. At the time Zipcar was using the mobile analog CDPD network for vehicle communications, which had a top speed of something like 19.2k/s and cost us around $1/month per KB of data. However, it also had a limited number of data channels, and since it used the old AMPS network broadcast in the 800 - 900 MHz range. I happened to have an amateur radio license and a radio that was able to receive in that band. Since we were still in contact with the missing car we knew it hadn't been chopped (yet) and I figured we might be able to use some sort of radio direction finding technique to locate the car. My friend and fellow engineer Carl was able to reprogram the firmware of our embedded electronics to tell us which cell tower the car was in contact with, and with that we could look up the FCC id in their database to find the tower's street address. So my boss Roy and I hopped into his car and drove to Long Island. We drove up to the tower, and I leaned out the window of his minivan with a yagi antenna and my radio (set to scan the 40 or so CDPD channels.) We asked Carl (back in Boston) to start pinging the car. To the radio this sounded like a half-second burst of static, but since it was very regular it was also very easy to identify. Sure enough, after driving around for a few minutes we picked up the signal. pffft pffft pffft We drove around the tower in a wide circle until the signal was the strongest, got out to scan the area, then used the new bearing to reduce the circle. Eventually we ended up in the parking lot of the Long Island railroad. There in the back corner was our car, luckily unscathed and none the worse for wear. Ping rocks. |