Most nanny camera systems are usually disguised and have a lux factor of 1 and 3.77mm CMOS. They are also powered by lithium, weigh half a pound and they capture still images. However the smoke detector has a more superior frame rate and is pricier. Always add a DVR system so you can review the captures videos later. Some cameras might like an alarm system detector and the DVR can be mistaken for stereo speakers. Clarity might not be an issue in terms of choosing your surveillance cameras as there are only a few people involved. Features you will most likely invest in would on how long the camera can store the videos and on how long it can last without recharging the batteries. On the other hand, motion detection cameras are best for babysitter cameras as it will only record whenever there is movement detected.