An urbex alarm is a motion detector or alarm that is used to detect movement in abandoned buildings or other locations that are off-limits to the general public. These alarms are often battery-powered wireless infrared detectors that have a 40-60 degree arc out to 30 meters, which means they can detect movement from a distance. When triggered, these alarms can emit a loud noise to alert security or law enforcement of a possible intrusion.

Its worth noting that urbex is the practice of exploring man-made structures such as abandoned buildings or construction sites, often involving breaking and entering. Urban explorers may encounter silent alarms, which are insidious because they are hard to spot and are designed to be silent. These alarms can be used extensively by government agencies and private companies for state-of-the-art automated security systems.

In summary, an urbex alarm is a motion detector or alarm used to detect movement in abandoned buildings or other off-limits locations. When triggered, these alarms can emit a loud noise to alert security or law enforcement of a possible intrusion.