test and measuring instruments, namely, analog oscilloscopes and digital oscilloscopes, spectrum analyzers, AM/FM and audio signal generators, synthesized and function generators; digital multimeters, programmable and regulated direct current power supply, programmable electronic loads, ground continuity testers, withstanding voltage and insulation testers, high frequency noise simulators, lighting surge generators, inductor capacitor resistor digibridges, passive components standards, alternating current power supply; automatic test equipment, namely, in-circuit testers, auto-loading in-circuit testers, in-line type in-circuit testers; environmental test equipment, namely, temperature and humidity chambers, walk-in chambers, thermal shock test chambers, vibration testers; intercom systems, namely, room stations comprising, intercoms, video and audio monitors, computer hardware; sub-door stations comprising intercoms, video and audio monitors, computer hardware; building entrance stations comprising intercoms, video and audio monitors, computer hardware; security guard stations comprising intercoms, video and audio monitors, computer hardware; video distributors, multi-entrance controllers, message indicators; security systems, namely, security stations comprising intercoms, video and audio monitors, computer hardware; repeaters; converters; security control stations comprising intercoms, video and audio monitors, computer hardware; magnetic contacts, fire detectors, gas leakage detectors, panic alarm buttons, passive infrared rays detectors, access controls; public address systems, namely, pre-amplifiers, mixers, power amplifiers, control units, remote control panels, microphones, and loudspeakers