ShopAlerts

Technology by a company called PlaceCast

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video explanation

ShopAlerts™ is an opt-in, location-based mobile marketing solution that delivers highly relevant SMS messages based on location, time, CRM data, and user preferences. Combining location-based technology with the scalability of SMS, ShopAlerts delivers relevant offers and drives customers into physical locations. Today, ShopAlerts™ can locate more than 268 million phones in the U.S., or 92% of all consumers.

Basically, you opt-in, then based on which cell tower is communicating with your phone, they send you SMS offers.