The basic version from BT only includes the bell, no wiring instructions, no cable, no clips etc. It needs to be fitted by an engineer. SXEY Electronics Ltd though have combined the BT bell with their...
AdvantagesFree (or cheap if you buy the full version)
AdvantagesExcellent down to earth teaching.
DisadvantagesNot for everyone.
Advantagesprices, performs well, lasts long