If you are still under the impression that hidden cameras are just a part of the James Bond movies, then, you will have to come back to reality because these devices have a number of applications and are ordered in large numbers and discreetly.
Yes, whether you want to check on whether the babysitter is doing her job or if your spouse is cheating on you, these devices can be used to collect incriminating evidence. Of course, this is just for personal use but there are times when a journalist would carry hidden cameras wireless when meeting people. This, yet again, has brought out several underhand dealings to light especially when exposed to the masses.
And then there are the proverbial military cameras that are used for defense purposes and are far more extensive and advanced when it comes to the technology that is being used these days. It is not new that a lot of countries do a competition of sort in their desire to invest faster, better, and sophisticated devices that will eliminate the competition and will give them that edge.
Yet when it comes to civilian use, you can easily find spy cameras for home in stores as well as over the Internet at nominal prices. These cameras are often designed to serve a particular purpose and help you find the answers that you need.