I did my rears about 2 months ago and just did the fronts yesterday. The sensor triggers at about 3/32 of pad remaining, so hopefully you can tell by looking.

The article by Hayaku is an excellent resource and is very accurate. Read the tool list as the 6mm & 7mm hex (allen) sockets and 16mm socket are not a part of most tool sets.

The rears were a piece of cake on my car. The fronts were easy as well except that the previous owner had the brakes done and they really cranked on the bolts for the caliper carrier brackets. I snapped a regular socket trying to break them loose and ended up buying an impact wrench to get them loose. The anti rattle spings were a little tricky to get back on, but not too bad.

It feels nice to have new shoes on the beast

Good luck
Dennis