I got a new bluetooth keyboard yesterday, and it is nice. However, one thing I didn't notice at the time of purchase is it does NOT have a backward slash key. I only found it out when I try to type an UNC path.
As always, Google came to rescue. It turns out you can type a backward slash using the ALT GR + # key combo (at least in Windows 10 where I have tried so far!).
Edited 2018-03-17: On Linux, it is ALT GR + - key
