This is a driver for the Tradfri Puck. The device has been discontinued, but people have been finding them for really cheap. Here's a pic. The top is magnetic and just pops right off.
After you join the device to HE and select this driver, run the Configure command.
It has a setting to choose modes: switch vs. dimmer.
The device will act like a switch/dimmer that has no load. You'll want to bind it to a light to use it. Two-way binding is important, so use my Switch Bindings app:
Previous discussions that led to the creation of this driver are in this thread: