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# Security camera motion sensing question

1. From what I understand of today's security video cameras, they have a method of motion detection where they compare different images from different times to detect if there's been motion, and then they start recording. Well, I tried an app on my smartphone that used that method, and it drained the battery real fast. I discovered by going to the email account that my phone was linked to. I found that the phone simply took a picture about every 2 seconds. When one picture would be different from a previous one, it was considered motion. But if that's how security cameras work (I mean actual security cameras as opposed to smartphone apps), then wouldn't that wear the camera/memory card out real fast?

Here's what I've found online on the subject. It seems to match what my conclusions are about how it works:

"motion detection is basically the process of comparing sequential images and determining whether the differences between them represent motion. If there are significant differences between two consecutive images, the cameras "conclude" that there has been motion within the camera view. They do this based on a couple important settings -- sensitivity and percentage." https://www.networkworld.com/article/2761095/it-management/how-motion-detection-cameras-work.html
2. That's how motion detection works. If abs(A - B) > threshold, where A is one picture B is the next, then there's motion.

Here's an example where one of our dogs was caught red handed mangling her bed while nobody was home:

On the left is the normal image. On the right is that frame subtracted from the previous frame, then the absolute value multiplied to make the differences more obvious. You can see that unmoving background is all black. The dog and cushion in motion show up as brighter areas.
3. Originally Posted by jagabo
That's how motion detection works. If abs(A - B) > threshold, where A is one picture B is the next, then there's motion.

Here's an example where one of our dogs was caught red handed mangling her bed while nobody was home:

[Attachment 45234 - Click to enlarge]

On the left is the normal image. On the right is that frame subtracted from the previous frame, then the absolute value multiplied to make the differences more obvious. You can see that unmoving background is all black. The dog and cushion in motion show up as brighter areas.
Understood. But doesn't this method wear out a camera/storage device by taking pictures for comparison so often? If it takes an image every second to compare to the previous image, it would be taking 86,400 images each day. Doesn't that take a toll on the camera? Are these cameras known for having short lifespans? Also, if the camera were battery-powered, wouldn't this drastically shorten battery life?

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