Patent ID: 8821451

Claim:
An automatic medicament delivery device that notifies a user of complete expulsion of medicament from a medicament container comprising, a) a tubular housing having a proximal end and a distal end; b) a container holder coaxially arranged and fixed on the proximal end of the tubular housing; c) a medicament container lodged within the container holder comprising a predetermined volume of medicament, a slidable stopper and a delivery member; d) a tubular extension member having an inner surface; e) a hollow tubular plunger rod having an outer surface slidably engaged within the inner surface of the tubular extension member, where the plunger rod has a proximal wall configured to engage and drive the slidable stopper in a proximal direction upon activation of the medicament delivery device; f) a first resilient member positioned inside the plunger rod, wherein the first resilient member is in a pre-tensioned state exerting a force on the proximal end of the plunger rod prior to activation; g) an engaging surface on the outer surface of the plunger rod; h) a resilient tongue projecting radially inward from the tubular extension member and releasably engaged with the engaging surface to prevent axial movement of the plunger rod in the proximal direction and to maintain the resilient member in the pre-tensioned state; i) a tubular operation member rotatably and coaxially arranged on the tubular extension member and having an inner surface engaged with the resilient tongue; j) an activation member slidably positioned within the tubular housing and rotatably fixed relative to the tubular housing, where the activation member is configured to engage the tubular operation member to activate the device; k) a second resilient member engaged with and exerting a biasing force on the activation member in a proximal direction; and l) a signal generating member that is configured to transmit an audible sound after activation to signal complete expulsion of the medicament from the medicament container through the delivery member.