AT&T is rolling out a new location-based ad service that sends you coupons when you need them most: at or near the store.

ShopAlerts is a free opt-in service available for everyone (not just AT&T customers) that requires only a simple sign up and your willingness to make your location data available. Once activated, AT&T will send you available deals whenever you're in the vicinity of a participating retailer. Currently the list includes: HP, Kmart, JetBlue, SC Johnson, Nature's Recipe and a few others. AT&T says partners will continue to expand in the coming months. Right now, you can use the service in New York, Los Angeles, Chicago and San Francisco, with more cities to be added later.

Similar location-based deals have been offered by apps like Foursquare in the past, but in most cases you were required to "check in" to a specific business before being made aware of any sweet specials. With automatic services like ShopAlerts, bargain hunting stands to become a lot easier and more seamless.