Inside of the hidden camera object (such as mantle clock, alarm clock, etc) is a pinhole security camera and a wireless video transmitter.
Depending on the object, the power might already be taken care of. For example, an alarm clock already plugs into the wall for power. A hidden camera would tap into that same circuitry so the only wire for power coming out of the device is the alarm clock factory power wire.
Other objects, ones that don’t connect natively to power – such as an artificial plant, will have a thing small black wire coming out of the plant base and it would be a foot or so long. On these devices, an AC power supply is included to plug into a regular wall outlet and then connect into that thin black wire.
Unfortunately, wireless hidden cameras do not mean that they don’t require power. Wireless hidden cameras (such as these from Advance Security), require power for operation, and this is accomplished by the above methods.