Buy a bug detector
For about $200, you can buy a gadget for finding spy equipment. Bug detectors are basically radio frequency scanners. As you sweep the antenna around the room, they hunt for the transmissions being broadcast by any cameras or microphones hidden in the room. Remember that cameras are often motion activated and microphones are typically sound activated; turn on your stereo and the lights before doing your sweep.
Once detected, you will still need to find the bug. Look for objects with line of sight to a large area of the room—these may have cameras installed in them. If there’s a phone in the room, check it for microphones first, and then sweep outwards. A mirror designed to hide a camera will appear partially transparent under close inspection with a flashlight.
Once you’ve found the bug, you have a few options. You can destroy it, which will be satisfying but will also alert the surveillance team that you’re aware of them. Far more fun is turning it against your observers, either by feeding false information to them or by giving them more than they bargained for. Make them watch you dance naked.
If you think you know what the surveillance team is after, this may be an opportunity to do away with them. Use their surveillance devices to feed them a plausible but false version of the information they seek; it may be enough to get them off your back. This tactic takes some planning and a good deal of time, but if you can casually provide them with all they think they need, they may back off.