Abstract: An apparatus and system for monitoring usage of one or more power tools, the system comprising setting means by which a prescribed extent of usage of a tool can be set. The prescribed extent of usage is determined by conversion of usage units into time units using a conversion function specific to said tool, wherein the conversion function is dependent upon operational characteristics of said tool. The apparatus or system further comprise sensing means for sensing usage of a tool, timing means for timing the duration of usage of the tool in accordance with said sensing means, and control means arranged to provide indication when the timed duration of usage of said tool reaches or exceeds the prescribed duration.