Scan for android devices in an area?

Just working on a concept for an app with a friend and I was wondering if technology exists or is feasible to scan for android devices in the area with the same app. So for example, if you and a friend walked by each other both with the app installed something X, Y or Z would happen depending. Mostly just wondering how the scanning would work, I know most phones have GPS enabled and I know most can broadcast wifi, just wondering if this is at all possible