An actuator device for engagement with an inhaler, the inhaler comprising an inhaler housing holding a pressurized canister of medicine and the inhaler having a mouthpiece; wherein: - the actuator device is in the form of an actuator housing into which the inhaler can be inserted in a clip-in manner and at least partially housed, such that the mouthpiece of the inhaler is accessible to the patient for insertion of the inhaler mouthpiece in the patient's mouth for delivery of the medicine; - the actuator housing is configured to extend along the entire length of the inhaler housing on the side opposed the mouthpiece; - the actuator device comprises a mechanism to operate the inhaler, the mechanism including a lever which is moveable between an "at rest" position and an "in use" position in which, in use, the lever exerts a force on the pressurized canister so as to operate the inhaler and release medicine from the pressurized canister, and an electrically driven linear motor to trigger the lever to operate the inhaler; - the actuator device comprises detecting means for detecting the presence of a patient to whom medicine is to be delivered from the pressurized canister and to activate the mechanism, wherein the means for detecting the presence of a patient comprises a breath activated sensor; characterized in that - the actuator housing is configured to extend circumferentially about a portion of the inhaler housing, at an end of the inhaler housing opposed the inhaler mouthpiece, to define an enclosed portion of the actuator housing, - the actuator mechanism is housed within the enclosed portion of the actuator housing; - the actuator housing comprises air vents provided on the enclosed portion of the actuator housing, whereby in use, when a user positions his/her mouth over the inhaler mouthpiece and inhales, air is drawn in through the air vents and said air flow activates the breath activated sensor; and - the actuator device comprises an internal timer circuit to control the activation of the lever to operate the inhaler, the timer circuit providing a delay before delivery of medication from the canister according to the patient's prescription. - the actuator device is in the form of an actuator housing into which the inhaler can be inserted in a clip-in manner and at least partially housed, such that the mouthpiece of the inhaler is accessible to the patient for insertion of the inhaler mouthpiece in the patient's mouth for delivery of the medicine; - the actuator housing is configured to extend along the entire length of the inhaler housing on the side opposed the mouthpiece; - the actuator device comprises a mechanism to operate the inhaler, the mechanism including a lever which is moveable between an "at rest" position and an "in use" position in which, in use, the lever exerts a force on the pressurized canister so as to operate the inhaler and release medicine from the pressurized canister, and an electrically driven linear motor to trigger the lever to operate the inhaler; - the actuator device comprises detecting means for detecting the presence of a patient to whom medicine is to be delivered from the pressurized canister and to activate the mechanism, wherein the means for detecting the presence of a patient comprises a breath activated sensor; - the actuator housing is configured to extend circumferentially about a portion of the inhaler housing, at an end of the inhaler housing opposed the inhaler mouthpiece, to define an enclosed portion of the actuator housing, - the actuator mechanism is housed within the enclosed portion of the actuator housing; - the actuator housing comprises air vents provided on the enclosed portion of the actuator housing, whereby in use, when a user positions his/her mouth over the inhaler mouthpiece and inhales, air is drawn in through the air vents and said air flow activates the breath activated sensor; and - the actuator device comprises an internal timer circuit to control the activation of the lever to operate the inhaler, the timer circuit providing a delay before delivery of medication from the canister according to the patient's prescription.