Backstory: Everyone enjoys connecting to free wifi when shopping or sitting at a coffee store (starbucks).
The Idea: Offer free wifi in exchange to track consumer buying habits.
Deep Dive: You would offer brick and mortar store customers free wifi in exchange for their email. They would be opting into this free wifi at every store you have this service deployed. You would track how long users spend in the store and aggregate the type of stores they visit.
Using this data you could have a backend platform where other advertisers can email or advertise on digital billboards in areas based on your buying data. You would need multiple large scale brick and mortar stores to adopt for this to really work.
Validation: This is similar to how facebook tracks your likes and interest and targets to feed you targeted ads.
Monetization: You would make money from advertisers and you may be able to charge the stores a minimal amount to provide free wifi to their customers.