An ignition interlock device is a small device (about the size of a cell phone) that is installed in a car that measures a person's BAC level. If a person blows into the device and it registers a BAC level that is above a certain amount, the car will not start. The driver must also give breath samples during the drive. Who has to get an interlock device following a Texas DWI arrest?
Currently (and this could change soon), Texas law requires interlocks as a condition of probation only for repeat offenders (2nd DWI or 3rd DWI) or those with blood-alcohol concentrations of 0.15 or greater in any alcohol-related driving offense (primarily DWI or DUI). The device also is required for those arrested for DWI and released on bail if they have had a previous DWI conviction - or if they hurt or kill someone.
An interesting side note. If you ultimately plead guilty to DWI charges in Texas, and if you choose jail time rather than DWI probation, no interlock device is required to be installed. Those put on probation and ordered to have an interlock device installed also have to pay for the device - which can average about $150 a month - so some find jail time more appealing.