I was isolated in the hotel during the wedding. Why is the red light flashing in the isolation room? Is it surveillance?

It may be a smoke detector, which flashes every once in a while, usually with a red light.

Common inspection and monitoring methods are: turn off the lights, close the curtains, turn on the camera function of the smart phone, do not press the shutter, do not turn on the flash, and use the mobile phone to walk around the room. If you find a red dot, you have a camera. If you have no red dot, you have no camera.