Why do we need such high end hand held detection devices?

Searching for the illegal use of mobile / Cell signals is becoming an increasingly important task during counter surveillance sweeping. Numerous eavesdroppers transmit information via mobile/Cell networks. The mass production of components for developers such as GSM, 3G, 4G/LTE and 5G modules, enables them to develop cheap and quick surveillance methods which have ultra-high quality sound, video or location transmission. Hidden cameras camouflaged as household appliances, toys or interior objects will most likely transmit data via mobile networks or Wi-Fi. Spy listening devices quite often have a slot for SIM-cards to enable them to function on a cellular networ