How to link two sensors?

Question

Electronics

How can this be implemented: two sensors (very small) are triggered if they are within a radius of 10-30 meters. On the basis of what these sensors can be made, maybe there are some solutions and in general what to start from in order to solve this problem? By "work" I mean, for example, the indicator lights up.
I don't understand electronics at all, I want to understand.

Answer 1

If you want to figure it out - take an Arduino and experiment. Fortunately, there is a sea of ​​documentation.
For a specific task, I would use wireless sensors like nrf24l01 with the same Arduino or a "bare" MK for review.

Answer 2

depending on what it is for and what are the financial constraints. For example, you can not use MK at all, but it will be more difficult, or you can use bluetooth and you don’t need anything at all except software and so on.