A security system that secures a building includes a weather detector for detecting weather conditions, such as thunder or high winds, which are likely to cause false alarms in sensors such as an acoustic glass break sensor, shock sensor and vibration sensor. The weather detector may include a sensing component that senses atmospheric conditions external to the building, such as temperature, pressure, wind speed and/or lightning. The weather detector may also include a component for receiving a data communication, such as from a radio, Internet, or telephone link, indicating that the weather condition is present in a vicinity of the building. The security system operates in a bad weather mode by requiring corroboration of intrusion detection signals from the sensors that can cause false alarms.