There is a wiki page fro Ankle monitor which is basically the same thing.
How the Scram Bracelet Device Works
The 8-ounce bracelet tracks the user's alcohol level through a process called "transdermal alcohol testing," which essentially takes samples from the hard-to-see layer of sweat that is on everyone's skin.
"It will detect just about any level of drinking event," says Kathleen Brown, spokesperson for Secure Continuous Remote Alcohol Monitor (SCRAM), which makes the bracelet. "But we will not confirm any event until it reaches a 0.02 blood alcohol content."
This is how the Scram Bracelet looks like.
For a home installation fee of just $60, the device records the level of alcohol either every 30 minutes or every hour, depending on the offender's probation guidelines.
How does it work? The SCRAM functions in conjunction with a wireless modem that installed in the offender's home. 24/7, the bracelet takes a reading of his/her alcohol level every 30 minutes or so, and the data is stored on a inside the bracelet. Once a day, they must get within thirty feet of the wireless modem so that this data is downloaded and transmitted to a monitoring service. Failing to download this information each day would be a breach of their probation.
In the time that the Scram has been used, authorities report that there’s been a high compliance rate among people not drinking.
But errors can occur too. Consuming some types of baked goods, such as raisin bread or sourdough English muffins, have triggered Scrams to report alcohol use by an offender. And being an electronics-based device, malfunctions can occur.
The SCRAM bracelet is a device specifically designed to monitor drunken drivers who are under judge's orders to maintain absolute sobriety. This happens, for example, when a repeat DUI offender is out on bail. More and more court systems across the country are using the SCRAM to ensure offender compliance.