Apple has paid around $20 million for the Silicon Valley-based startup, an anonymous source told the Wall Street Journal.
As we previously reported, Google recently added indoor maps as a key feature for its Android users, with maps of popular Aussie shopping centres and landmarks now available indoors.
iPhone compatibility is on the way, too.
That led to Apple's first public apology for an app (the atrocious Apple Maps), and heads rolled.
According to reports, WifiSLAM is roughly two years old, and its approach involves detecting the user's location in a building using Wi-Fi signals that already exist inside the building.
It's run by a team of two, Joseph Huang and Nav Patel, who will likely now be Apple employees, although this is yet to be confirmed.
It remains to be seen how long Apple will take to incorporate the WifiSLAM technology into its own Apple Maps app, and what Google has in store to next one-up Apple.