Theft-proofing a convertible with no steering lock

These seem pretty cheap, but you will need to get a cell phone account for it to use it.

[ame="http://www.ebay.com/itm/Mini-GPS-GSM-GPRS-Tracking-SMS-Real-Time-Vehicle-Motorcycle-Monitor-Tracker-USA-/301118847004?pt=US_Tracking_Devices&hash=item461c14f81c"]Mini GPS GSM GPRS Tracking SMS Real Time Vehicle Motorcycle Monitor Tracker USA | eBay[/ame]