The FerrAlert Solo is the smallest, lightest pre-screening ferromagnetic detector available. It is highly sensitive and features the patented technology of the FerrAlert Halo system. When close to the detector, six green lights turn on, indicating the FerrAlert is ready to scan. If any ferromagnetic hazard is detected, the green lights turn off, a short audio alert sounds, and the amber detecting lights flash at the location of the ferromagnetic hazard.