It is legal to own and use a hidden camera detector as these devices do not in any way interfere with operation of other devices. Hidden camera detectors are considered legal because they are designed to protect people’s privacy and safety. They are used to detect hidden cameras, voice recorders, and other devices and surveillance equipment that may be used to spy on people without their consent.
However, using signal jammers may be illegal depending on your state or country. If a device only operates as a detector it is not illegal in any way.