Opened up a random microsoft keypad. It has no names on it, which I hate.
but if you open the battery compartment, which requires a screwdriver, there's a label in here. Model 1558, FCC ID C3K1558.
opening the back, it's got one little PCB, and that's all.
The membrane to the front is held on with ultrasonic welding
The PCB is pretty simple. It's got a built in antanna, a couple mosfets, and two chips.
u2 is a 6-pin chip with the label "RAR" on it. Probably something voltage related, given the position.

The main chip is an nRF24LE1 from Nordic Semiconductor.
It's a microcontroller with 16 kilobytes of flash, 1 kilobyte of RAM, another 1.5 kilobytes of NVRAM, and it does 2.4 GHz wireless.

AND PUNCH OUT ANOTHER ENTRY ON YOUR CARD, IT'S AN 8051!

The datasheet doesn't say anything about bluetooth or wifi, so this probably talks a proprietary wireless protocol to a USB dongle of some sort. One I don't have, annoyingly.
and apparently this goes with the Microsoft Sculpt Ergonomic Wireless Desktop Keyboard and Mouse
@foone Indeed. My preferred ergonomic keyboard.