The letter bomb detector detects ferrous and non-ferrous metallic objects contained within envelopes or thin packages. Objects are screened from both sides as they are passed under the scanning bar, which is mounted across the top portion of the unit. Mail scanners are suitable for police stations, government buildings, high-security facilities, and large mailrooms. Most mail scanners are quite accurate and can detect suspicious items while preventing false alarms. They use an x-ray to scan the contents of a package and search for dangerous items.