RF safeguarding devices are used to control machine operations by detecting changes in the RF field. RF safety products include personal monitors, survey instruments, area monitors, and protective garments. RF personal monitors are devices worn on the body that sound an alarm when radio frequency (RF) rises above a preset threshold. RF survey instruments can detect all frequencies with equal sensitivity (a flat frequency response), or vary sensitivity as a function of frequency in accordance with a particular standard (a shaped frequency response). RF area monitors sound an alarm or send an electronic signal when RF levels exceed a preset threshold in an area such as a shop floor. RF protective garments provide significant protection (10 dB or more); however, they must be worn properly. RF machine safeguards include presence-sensing devices, which can sound a warning, change machine function, or stop the machine. RF safeguarding devices also include safety mats, safety gates, safety relays, and safety interlock switches.