The Bluetooth transmitter is attached to a printer circuit board, which Facebook says can only be installed by an original equipment manufacturer, according to FCC filings.

In other words, it's a component that will be integrated into some sort of device, which Facebook is keeping under wraps for now (much of the info in the filings is still confidential).

The filings, which were filed in June, come as evidence mounts suggesting Facebook is working on new consumer hardware. On Tuesday, Bloomberg's Mark Gurman reported that Facebook's Building 8 group was developing a video chat device and a smart speaker, similar to Amazon's Echo. Business Insider previously reported that Facebook recently patented a modular device that could function like a smart speaker with a touchscreen. 

There are a few clues in the filing that point to some kind of drone or telecommunications-related product. The filing is under FCL Inc, which is the name of the subsidiary that Facebook uses for drone-related technologies, such as its Aquila drone. And the contact name on some of the documents is Andrew Guhr, a Facebook lawyer whose LinkedIn bio describes him as Associate General Counsel, Telecommunications at Facebook.

Guhr's job description raises some intriguing possibilities for the mystery product:

"Advising on telecom laws and regulations around the globe on projects ranging from submarine cables, terrestrial networks, wireless networks, experimental technologies, and next-generation OTT services."