Longmont, CO Noise from Specific Sources: Car Alarm Limits (2026)

Longmont Municipal Code Chapter 10.20 sets nighttime and daytime maximum sound pressure levels measured 25 feet from the source: 50 dB(A) nighttime and 55 dB(A) daytime in residential zones, 55 dB(A) nighttime and 65 dB(A) daytime in commercial zones, and 75 dB(A) around the clock in industrial zones. Section 10.20.100.D lists exemptions from those limits for specific operations, and subsection D.5.i places "warning or alarm devices that have the purpose of signaling unsafe or dangerous situations or calling for police" outside the ordinance entirely. A car alarm going off, whether from a break-in attempt, a bump, or a sensor malfunction, falls squarely in that category, so the city cannot cite a triggered vehicle alarm for exceeding a decibel threshold or for sounding during quiet hours the way it could a barking dog, a power tool, or an amplified speaker under the surrounding sections of the same chapter.

The second half of the picture sits in Chapter 6.98, Private Alarm Systems, which is Longmont's registration, monitoring, and false-alarm-fee framework for burglar and fire alarm systems installed on buildings. Section 6.98.020 defines "alarm system" for that chapter and then carves out three categories of device that do not count, the third of which is "alarm devices affixed to motor vehicles." Because a car alarm is defined out of the chapter, none of Chapter 6.98's obligations reach it: there is no requirement to register the alarm with the police department, no emergency contact card to file under section 6.98.040, and none of the escalating false-alarm charges set out in sections 6.98.050 and 6.98.060 that apply once a building alarm system rings three or more false alarms in a calendar year and becomes an "unreliable alarm system." Those provisions, and the 6.98.070 penalty of up to $500.00 for a chapter violation, are written for premises alarms and simply do not reach a device wired into a vehicle.

That leaves a car alarm functionally unregulated in Longmont: it can sound for as long as its own circuitry runs, at whatever volume it emits, at any hour, without triggering either a noise citation under 10.20.100 or a false-alarm charge under 6.98.050. The only recourse for a neighbor annoyed by a repeatedly malfunctioning car alarm is the general nuisance and civil-enforcement route in section 10.20.110, which lets the city attorney seek an injunction against a public nuisance in court, a much slower and heavier tool than the citation process used for other noise sources.