Day 62: House Arrest

Now that I am in the final month, I was able to meet with the County Probation Office, which is what handles the House Arrest process. I and three other prisoners met with a young guy from the office who [literally] read the rules to us.

Most of it was what I expected. No guns; no booze; you must notify your P.O. of your work schedule. You are permitted to go to the grocery store and doctors in addition to work, but not permitted to mow your lawn. You are required to comply with all Federal, State, and Local laws, although I am not sure how you are supposed to comply with weed-height ordinances if you aren't allowed to do yard work. Maybe city hall is bending to the powerful Lawn-Care Services lobby.

Oh, of course you are permitted to go to church, but not any other sort of hobby meeting.

I was able to slip in a question about the manufacturer of the monitoring devices while the guy was explaining how it worked. Based on his description, I believe I will be using the BI 9000 Series. Their company site is worth a look; it definitely is more polished than some of the other companies involved in the big business of imprisonment. On at least one of the product data sheets they refer to the people forced to wear these devices as "customers". One almost can imagine these people are marketing GPS location devices for luxury cars.

So the unit will be connected to a traditional landline - VOIP over DSL or cable Internet will not work. The P.O. will login to the BI website and create a schedule for me. Regularly, BI Inc's computers will dial into my device and download the log of when I cross the perimeter, comparing it to my schedule. I would expect it permits a certain amount of flexibility - I can not imagine P.O.s want to be notified every time I leave for work one minute late - and registers exceptions which it then reports to the P.O..

The perimeter is established by making me stand at each corner of my house and then configuring the device. While it is possible that the devices have a GPS receiver, based on the monthly price I will be paying, and the description of the hardware, the ones we will use appear to be a simple RF transmitter (ankle) and receiver (base unit). This means it probably only recognizes distance based on the time it takes for the signal to reach the base. Without two other units, it will not know location, so if I place the base unit strategically, I should be able to do some simple geometry and identify the true border and gain access to my back porch.

Most of that is deduction based on what I know and what info I can glean from publicly available information. But it is probably right.

Other, more interesting, opportunities for exploit are possible. If the device were extremely sophisticated, it might use public key cryptography to ensure the base can verify the anklet is the right anklet, but not visible to someone snooping the transmission. Although it probably just broadcasts an ID signal using spread spectrum, which is probably good enough to prevent the average electronic hobbyist from emulating the broadcast. If this sentence was for more than 90 days, I might build a spread-spectrum receiver and see if I could capture the signal and then emulate it.

But instead I will probably just end up playing a lot of XBox and PS3 (or the amount Brenda will tolerate).