Abstract: A sobriety interlock for a machine such as a vehicle operates in either an interlock mode or a BYPASS mode. In the INTERLOCK mode, a breath sobriety test must be passed before the machine can be started, while in the BYPASS mode, a breath test is not required to start the machine. When the system is powered up, it operates in the INTERLOCK mode for a predetermined period, preferably about 12 hours before automatically beginning operation in the BYPASS mode. From the BYPASS mode, INTERLOCK mode operation can be selected at any time by actuating a switch which locks in INTERLOCK mode operation for at least the predetermined period of time.