The present invention relates to a monitoring unit (200, 302) for a medicament delivery device, which monitoring unit comprises a housing (202, 300),- monitoring circuit (400) arranged in said housing (202, 300), capable of detecting and monitoring functions of the medicament delivery device,- attachment mechanism provided arranged with releasable locking elements (208, 306), a mechanical interface (231, 318) arranged to interact with a mating mechanical interface arranged on a medicament delivery device, and- an activation switch (242, 320) arranged to activate said monitoring circuit (400).
