Location-based ad and alert companies Placecast and Location Labs have teamed up to send shopping alerts to more than 180 million consumers across multiple cell phone networks.

The companies are creating ShopAlerts, which are location-triggered text messages sent from brands to consumers who opt into the service. The companies claim they can use the service to reach as many as 60 percent of U.S. consumers. The two companies are working on ShopAlert brand campaigns for retailers such as The North Face. More brands are signing up on a monthly basis, the companies say.

Placecast’s ShopAlerts service is a white-label mobile marketing tool. Retailers and other direct marketers deploy the technology to create their own version of the service. Consumers who agree to receive the messages can opt into them while they’re at a store, online, browsing text messages, or visiting mobile web sites or social networks. Once ShopAlerts are activated, the service automatically alerts the consumer about a brand’s local sales, special events, or other relevant information based on their location.

Combining location information and target marketing is called geo-fencing.

Location Labs allows Placecast to locate phones using its Location-As-a-Service Platform. The platform lets developers incorporate real-time location of smartphones and feature phones based on data from carrier partners. It does not require end users to download an app to their phone. Placecast CEO Alistair Goodman said the partnership with Location Labs gives the company a much greater reach than it would otherwise have.

Placecast was founded in 2005. It raised $8 million in a second round of funding in March. Investors include Quatrex Capital, Onset Ventures and Voyager Capital.

Some rival services such as ShopKick are based on apps, which only a small percentage of people are likely to have downloaded. Another rival is Xtify, which also does geo-relevant mobile messaging.