[lallysingh]

Or a camera pointed at the button

[majormajor]

Less invasive potential starting point: compare number of impressions with number of sales, look for suspicious outliers. More sophisticated options could be derived from similar easy-to-get numbers, too, like amount of foot traffic, door openings, etc.

[gowld]

But this would never happen, since the gimmick is to deploy a system to generate vanity metrics, not solve any problems.

[taneq]

If it's on a tablet, it probably has a front-facing camera taking snaps every now and then.