A compliance monitor (8, 26) configured to monitor patient usage of a medicament inhaler (1, 21), the medicament inhaler (1, 21) including: a store of medicament; a first housing (3, 33) for housing the store of medicament; a medicament dispensing means (4, 5) for delivering a dose of medicament; a mouthpiece (6, 24) for directing the dose of medicament into the mouth of a user; and a removable and replaceable cap (7, 25) for the mouthpiece (6, 24); wherein the compliance monitor (8, 26) comprises: a) a cap detection means configured to signal when the cap (7, 25) is covering the mouthpiece (6, 24), and to signal when the cap (7, 25) is being removed or replaced with respect to the mouthpiece (6, 24); and b) a dose detection means configured to signal when a dose of medicament has been dispensed; and characterised in that: the compliance monitor (8, 26) is configured to determine the occurrence of a first or second user error in dose delivery based on the signals received from the cap detection means and the dose detection means, wherein: a first user error is determined if the cap detection means signals that the cap (7, 25) is removed or replaced with respect to the mouthpiece (6, 24) at substantially the same time as the dose detection switch signals a dose of medicament is dispensed; and a second user error is determined if the cap detection means signals that the cap (7, 25) is covering the mouthpiece (6, 24) at substantially the same time as the dose detection means signals a dose of medicament is dispensed. a store of medicament; a first housing (3, 33) for housing the store of medicament; a medicament dispensing means (4, 5) for delivering a dose of medicament; a mouthpiece (6, 24) for directing the dose of medicament into the mouth of a user; and a removable and replaceable cap (7, 25) for the mouthpiece (6, 24); wherein the compliance monitor (8, 26) comprises: a) a cap detection means configured to signal when the cap (7, 25) is covering the mouthpiece (6, 24), and to signal when the cap (7, 25) is being removed or replaced with respect to the mouthpiece (6, 24); and b) a dose detection means configured to signal when a dose of medicament has been dispensed; and characterised in that: a) a cap detection means configured to signal when the cap (7, 25) is covering the mouthpiece (6, 24), and to signal when the cap (7, 25) is being removed or replaced with respect to the mouthpiece (6, 24); and b) a dose detection means configured to signal when a dose of medicament has been dispensed; and characterised in that: the compliance monitor (8, 26) is configured to determine the occurrence of a first or second user error in dose delivery based on the signals received from the cap detection means and the dose detection means, wherein: a first user error is determined if the cap detection means signals that the cap (7, 25) is removed or replaced with respect to the mouthpiece (6, 24) at substantially the same time as the dose detection switch signals a dose of medicament is dispensed; and a second user error is determined if the cap detection means signals that the cap (7, 25) is covering the mouthpiece (6, 24) at substantially the same time as the dose detection means signals a dose of medicament is dispensed. a first user error is determined if the cap detection means signals that the cap (7, 25) is removed or replaced with respect to the mouthpiece (6, 24) at substantially the same time as the dose detection switch signals a dose of medicament is dispensed; and a second user error is determined if the cap detection means signals that the cap (7, 25) is covering the mouthpiece (6, 24) at substantially the same time as the dose detection means signals a dose of medicament is dispensed.