The Micro Scout brick is included as part of two kits, the Lego Droid Developer Kit (9748) and the Dark Side Developer Kit (9754). The only difference is the colour of the brick: white in the Droid kit, grey in the Dark Side kit.
This electronic brick was intended to be programmed by the Lego Scout brick or Spybot brick but anything which can generate the low speed light pulses of the Visible Light Link (VLL) protocol can be used. The RCX brick can also be used to program it. The Micro Scout has a P mode to process VLL commands - the select button cycles through the modes.
The Micro Scout is powered by 2 AA batteries. If you are digging one out of the attic or buying one second-hand from Jawas then it's important to check that there have been no battery leaks. A caustic leak can damage the printed circuit board (PCB) particularly if the Micro Scout has not been stored face-up. The original manual contains some sage advice:
Always remove the batteries from the battery box for long-term storage or if they have reached the end of their life. Liquid leaking from dead batteries will damage the battery box.
If you need to fix a Micro Scout brick this section may help.
There are four screws which are easily unscrewed to open up the brick. The blue screen clips into the battery compartment and is easy to unclip. The circuit board is more difficult to remove as there are two terminals which need to be desoldered.
This shows the PCB which has been cleaned to remove the alkaline deposits from a substantial battery leak at the negative terminal. The through-hole plating is damaged and partially missing leading to poor connectivity for the ground. This damage caused the Micro Scout to work intermittently.
There are a few options to repair this, the easiest approach for this particular case is to scrape away some lacquer and solder a small wire (not shown) from one side of the PCB to the other to ensure the negative terminal connects to the ground and ground plane on the other side of the PCB. Inelegant but effective.