I had no idea this was happening. Somewhat amazed at data sciences, and somewhat creeped out. Here's an example of what they can gather if you leave your WiFi on:
The average wait time at the back register is two minutes. Half of your customers have been in your store twice in a week. Ten percent of the people who come in your store never come near a register, meaning they don't buy anything. There are a lot of people not finding what they want. The big promotion on the east side entrance of your store was more successful at bringing people to purchase than the promotion on the west side of your store. Here's the hotspot in your store that draws the most users. The typical user comes in and purchases one thing. Ten percent of your users have been at more than one of your stores.
Read
more in Washington Post.
(Thanks, Phil)
