Updated with info from BFD.
An annual event that lets car enthusiasts show off their modified rides at the Post Office Square garage ended a bit early when the Boston Fire Department arrived to figure out why smoke detectors went off and wound up evacuating the garage due to elevated carbon-monoxide levels.
More than 200 Masstuning enthusiasts had gathered on level 3 of the six-floor garage when the alarms went off around 8 p.m. A Fire Department spokesman reports: