A device (1) for automatic injection of a product into an injection site, the device (1) comprising:a housing (9) having a proximal end and a distal end；a flexible part (10) at the distal end of the housing (9) projecting inwardly and toward the distal end of the housing (9) in a non-deflected position, the flexible part (10) transitionable between the non-deflected position and a deflected position；a piston rod (7) movably disposed within the housing (9)； andan intermediate part (12) mounted around the piston rod (7),wherein as the intermediate part (12) is moved axially towards the distal end of the housing (9), the intermediate part (12) deflects the flexible part (10) outward to the deflected position, and once the intermediate part (12) is advanced beyond the distal end of the housing (9), the flexible part (10) returns to the non-deflected position thereby generating an audible indication.
