Keep in mind the following when considering a hidden camera:
Environment - Indoor your options are plentiful. Outdoors not so much. Try to find something that suits the location. A clock radio hidden camera may not look over a fireplace mantel. A hidden camera can opener does not belong on an office desk. You get the picture.
Power - We get many requests for wireless cameras. A camera requires power and either a recorder or a wireless transmitter that send the signal from the camera to the recorder or viewing post (not so common). This requires substantial power and we usually recommend that you wire power to the device if possible. If not possible and battery is the only option for your hidden camera, then you need to look at battery life. The smaller the device, the less likely there will be much battery. Our Zetta brand and a few others are excellent choices for battery only options. We can custom make battery powered devices but they will require large housings for batteries if you expect the battery to last. Our Xtreme Life line also does a great job of utilizing battery power. These can last a long time in a dormant state and record only on motion. Typically, wireless transmissions will require much larger battery power and size. Only expect a couple hours from a battery powered wireless device.
Recording Length - Be sure you choose the right size memory card or storage size when recording hidden video. Storage is getting cheaper and there are many options available for a small cost that we were very pricey a year ago.