Several years ago a local non-profit organization contacted me about helping them with a service they were providing the community. This non-profit takes donated vehicles, fixes them up and sells them a hair above cost to individuals that have "less-than-perfect" credit. This non-profit provides all the financing to the individuals and when the monthly bill is due they would also take that opportunity to teach the vehicle owners basic car maintenance.
When this program first started out they were struggling to keep it afloat. You see many of the individuals with "less-than-perfect" credit got that way because they had a hard time prioritizing their bills and this non-profit was having an 18% default rate on the financing they were providing. Since they could not afford to repo these vehicles, the non-profit started using "payment protection" devices. These devices are Starter Interrupt Devices that behave like an alarm clock except they count down to 0... like a bomb. Instead of blowing up when they hit 0 they disengage a relay that is connecting the ignition key to the vehicles starter; thus preventing the vehicle from starting again once it is shut off.
This sounds very 1984 "Big Brother-ish", but these devices help the individuals make paying the monthly car payment a higher priority. Once these devices were installed this non-profit went from the 18% default rate down to less than 2%. This non-profit's program is now one of the few similar programs in the state that is completely self sufficient and relies on no state or federal funding.
Where I came in was the non-profit was not happy with the Payteck device they were currently using. It was too expensive, complicated to use, and relied on a keypad in the vehicle to update the new payment due date. This keypad was constantly breaking due to pop spills and other abuse.
The design was based off of a Silicon Labs C8051F300 8-bit micro and a (now obsolete) Maxim MAX6902 Real-Time-Clock. The circuitry is pretty straight forward: a LM317 regulates the vehcile's voltage down to 3.5V, the MAX6902 keeps track of the time, date, and alarm date in its CR2032 coincell backed RAM, a RS232 port connects the device to a PC, and a buffered SPI bus connects the micro to the EEPROM dongle.
The 2-sided 2-layer PCB was laid out using Cadsoft's EagleCAD.
The C code to control the device was written using Silicon Labs IDE and an open source compiler, SDCC. It took a bit of work converting the original code I started writing in Keil to SDCC, but the price tag was right. SDCC's code is about 2x as big as the Keil code, but 8KB flash was enough to get the job done.
I also wrote a Windows app with Visual Studio 2005 to program the devices time, date, alarm date, and program the Key Chain EEPROM dongles via a com port.
Overall the non-profit was happy with how these devices turned out and bought 27 of them from me. I was also very pleased with how well these devices worked. On the next revision I'd like to get rid of the RS232 port and replace it with a USB device port. Replacing the custom EEProm dongles with SD Cards or USB flash drives would be nice as well.
There are quite a few companies that manufacture these Starter Interrupt Devices and they span simple devices like mine all the way up to GPS & Mobile Phone enabled units that can be reprogrammed wirelessly. The letigation is interesting to read about as well. Many of the companies have been brought to court for "endangering" the driver when the device disables the starter. Based on what I've read the Starter Interrupt manufacturers have always won the court cases, becasue these devices don't shut off the vehicle, they just prevent it from starting. Also everyone of these devices including mine have an "Emergency 911" way of starting the vehicle a limited number of times in case of emergency even if the payment date has passed.
Anyway this is interesting "Behavior Modification" technology and even though it is a bit "Big Brother-ish" it does enable people with "less-than-perfect" credit (i.e. scores less than 400) to finance a vehicle.