The invention relates to a device (1) for automatic injection of a product into an injection site, the device (1) comprising: a container (2)； ； a tubular housing (9) having a at least a flexible part (10) located at said distal end, defining a first opening at said distal end； a piston rod (7) located in said housing (9)； an intermediate part (12), wherein, with sufficient distal displacement of said piston rod (7), said intermediate part (12) causes said at least a flexible part (10) to deflect outwardly and with further distal displacement of said piston rod (7) causing said at least a flexible part (10) returning towards said at rest state generating a sound.
