Sensors distance

I have a project that requires a sensor to alert when someone moves away from a predesignated spot.

You are going to have to sit down and actually define some requirements before you are going to get anywhere.

What range does it have to work at?
Daytime or at night too?
Define “moves away from a predesignated spot” - by how much? a foot, meter, what?
Are there other people moving around in the same space?

Part of any project is to define what the requirements are - until you do that, you can’t move ahead because you don’t know what you really want to do.

Thank you for the prompt response.
The range would be between 1 and 2 feet.
Both day or night
It would be one person moving away from the spot.