While these aren't new technology, and have been around awhile, prices have become pretty reasonable, and some of them have gotten very sophisticated. You can get everything from still photo cameras that are only good for daytime use to infrared nighttime still cameras that work even in extremely low light, to day and night time video cameras. Most of them have motion detection, and are good for hunters looking to see what animals are crossing their favorite hunting grounds, without having to sit and watch in the pre-season, to someone who just wants to know what is prowling around outside the house in the dark at night.
Some sell for as low as $69, with some as high as a $1000, and with all the different options, there is sure to be something for everyone. They are also weatherproof, and most of them come with a long lasting rechargeable battery, so you can leave it outside for days or weeks on end, and then when you want to see what it has captured, most of them have an SD card, like digital cameras use, so getting the images or video is fairly easy.
The first time i saw one in use, my in laws had a night time still image version set up outside their house, for capturing deer running through the back yard after dark. We used one that did video, on a recent camping trip, and captured a bear on video near our camp site.