Apple Inc.'s latest product to carry the "i" prefix—following the iPhone and iPad—promises to do for indoor spaces what GPS did for the outdoors.

Apple's iBeacon allows apps to locate a user within a few inches, so that a phone can direct a driver to the nearest open spot in a parking garage or the shortest hot-dog line in a crowded stadium. It allows restaurant diners to pay the check and leave without a waiter's assistance or museum-goers to learn about exhibits by walking past. Soon, it might make shopping-mall...