The Security Cameras in Phasmophobia are dependent on the location you are investigating. All locations have at least one Security Camera. The houses have only one, which you will likely find to be useless. I've not found the ones in the High School or the Asylum of much use either.
However, the Security Cameras at the Prison are very useful. I have on many occasions found Ghost Orbs on the Security Cameras before I've even picked up the key. This can save a good amount of time and start you off with evidence in your journal before you even leave the truck. It's worth the few minutes it takes to check them. Keep in mind that you will only see Ghost Orbs if you use the Camera's Night Vision mode. We've even spotted the bone a few times with the Prison Security Cameras.