Maintenance and expected lifespan
If not accidentally or intentionally abused, most good hand-held metal detectors will require no maintenance. Extended maintenance contracts are usually not required beyond the initial warranty period. The only in-house maintenance that will be required is to provide for the recharging of batteries each night and/or making certain that new batteries are always available.
Most good hand-held metal detectors should have a useful lifespan of about 5 years, much more if used infrequently and possibly less if in constant use.
Research Report: The Appropriate and Effective Use of Security Technologies in U.S. Schools