Wouldn’t a portable detector be enough to detect the spy bug? Is this constant detection system a must?

Hacking devices and methods are becoming more and more advanced.  They can now be set on/off and controlled from a distance outside. If the hacker sets the spy bug off while a portable detector is trying to find it, it can never be detected. With this constant detection system,  24/7 operation and detection is possible. Coupled with the existing 24/7 on-line security, the organization can counteract the persistent  hacking threat.