[oakey46]

Just for info, I had my X1 (25600 miles) in to the UK dealer for some very minor warranty work earlier this week. As part of the process the technician carried out a 'Vehicle Health Check' from which he reported an 'Advisory' that the front brake pads were down to 6.0mm (discs OK) and rear pads down to 4.0mm (discs OK). I don't know at what wear stage the warning light would show.
Quoted UK prices for complete pad replacements were Front £260.24 and rear £234.31. Ouch!!!
Additional info: I just checked a UK parts supplier and indicative prices for the front replacement pads and wear/ABS sensor (both parts required) shown as £121.03 for Brembo pads and Pagid sensor) and £105.83 for similar rear parts. It appears the sensors are at front left and rear right brake unit. As stated, those prices are indicative and may be different depending on manufacturer of brake pad assembly unit (as was the case on my previous Audi Q3).
No doubt genuine BMW parts would cost more, plus dealer labour charges, but while X1 still within warranty period (UK 3 year unlimited mileage) I shall most likely just have to tolerate the dealer cost.