Tezza1958
I use a Sena SMH5, no drilling involved, reasonably priced, always got on well with it, it interchangeable between helmets, so I have speakers in all my helmets and one bluetooth unit which I put on the helmet I am using, it just slides on a plate which is stuck to the helmet.
Deleted Member
I use an Interphone Link which is similar in spec and price to Tezza's Sena. The bluetooth unit attaches to a plate which is either stick on or clamp on depending on your helmet, definitely no drilling. I use the stick on pads on my Shark helmets. The Link is the low end unit from Interphone's offering with a range of approx 200 metres bike-to-bike, not really enough if you're intending to use it for group touring but I don't do that and I find it works well rider-to-pillion and for phone or satnav. It also has a built in FM radio but that's a feature I don't use.