It's Maplin's product code: GW57M.
I have one under the dash on my 1150 with the external sensor glued under the front of the beak (I've also shortened the sensor wire but cutting, soldering and shrink-wrapping).
As others have said, they stop working when you wash the bike (but I've never had a problem when riding in the heaviest rain), but they do come back when they have dried out a bit.
At under £8, it's a handy item.
Greg