"In other than one- and two-family dwellings, system detectors or singleor multiple-station smoke alarms should be subjected to a sensitivity test within one year after they are installed. The test is intended to ensure the sensing chamber remains calibrated within the sensitivity range established by the manufacturer. If a detector is too sensitive, it will be susceptible to nuisance alarms. If it is not sensitive enough, it may not operate in the presence of smoke. According to the National Fire Protection Association (NFPA) 72, 'National Fire Alarm Code'®, the sensitivity should be checked and calibrated every alternate year after the first test. If, however, after the second required calibration test, sensitivity tests show that the device has remained within its listed and marked sensitivity range (or 4-percent obscuration light gray smoke if not marked), the length of time between calibration tests may be extended to 5 years."
Coffee Break Training - Fire Protection Series No. FP-2011-3-REV1
United States Fire Administration: http://www.usfa.fema.gov/