Nearly all Major League Baseball parks and around half of pro football, basketball and hockey arenas are dotted with beacons and other technologies that communicate with mobile devices to track fan footpaths, encourage them to upgrade seating, and connect with them on behalf of sponsors during and after the game, according to proximity sensor research provider Proxbook.

The company's new quarterly report shows that 93% of MLB parks, 53% of National Basketball Association arenas, and 47% of National Football League stadiums deploy location trackers.

The quarterly report is an extension of the Proxbook directory of proximity technology firms organized by Unacast, a firm that partners with those tech firms, connecting the location information they glean to ad exchanges.

"This is not a pilot," said Thomas Walle, CEO and co-founder of Unacast. While retailers have been big adopters of proximity tracking technology, professional sports is "by far the vertical with the highest penetration of beacon deployment," he said.

Teams including this year's NBA finalists, the Golden State Warriors and champion Cleveland Cavaliers, are among many using location tracking in their arenas. The Warriors, for instance, used beacons to trigger seat upgrade offers to people as they enter not-as-desirable sections of Oracle Arena, according to the report. The offers, sent to mobile phones with the Warriors app, include trackable links that helped the team determine the percentage of seat upgrades prompted by beacons.

"It's a great way for a team to make some incremental revenue," said Mr. Walle.

In another NBA example, The Milwaukee Bucks served content from McDonald's in the team app when people approached geofenced McDonald's locations.

European football teams are also using proximity technology in their home arenas.

MLB began testing beacons that communicate with its At The Ballpark app during the 2013 off-season at Citi Field, home of the New York Mets. The early concept was to welcome fans when they enter the vicinity, surface historical information and potentially enhance sponsor messages and displays with advertiser content.

The number of proximity sensors placed in physical spaces across the globe appears to be growing rapidly. The number rose to about 8.3 million in the most recent report, up 33% from the report three months earlier. Proxbook data is based on voluntary self-reporting by companies involved with sensor services.

Most of the sensors in Proxbook's new report, about 6 million, are beacons. Around 2 million are near-field communication sensors, while the small remainder are Wi-Fi points.