Smart devices that can withstand a power outage and reconnect

Not a bad idea with cameras, as crooks are know to switch off power or pull fuses.

Or cut wires.. possibly near the camera....

"Or cut wires.. possibly near the camera...."

Two cameras pointed to each other, and stream video to the cloud.

Or a lick of paint on the lens...,  (paint-gun?)...  ( well this about electric sustaining, not howto hack a security system... ).

So, if you are adding a camera to spot mischief then I'm not sure adding a UPS is the way to hide the camera. UPS's tend to be big. Even the smaller UPS's are still 10x bigger than the camera. If I were a criminal, I'd see that pretty quickly, further most criminals are dissuaded from mischief when they see camera's around the home on the outside. They don't go looking to cut the power and/or shoot the cameras with a paint gun. Most criminals are not very smart and dont have any tools to do anything. They'll pick up a rock from your property and break a window and enter that way. Rather if they see anything security related, they simply move on to a neighboring house which doesnt have any of that. Another suggestion I know works and is very cost effective is to purchase a Sign for a security company (I got mine from Ebay). They usually come with stickers you can place doors and windows. Just recently, my neighbors car was broken into and my car was left alone. He just last week added a security sign to his front yard and stickers to doors and windows. You might think it wont work, but it does.

The UPS is hidden inside of the house, under a desk in the office, hooked up to a POE switch or camera PSU and the router.

Only the cameras are visible from outside. Cameras cover each other. Stream straight to the cloud.

Simple!