(57) A device for monitoring the displacement of a bunch of banknotes protected in a bank comprises, concealed in said bunch, an electric battery (1), a coded controlled frequency electromagnetic wave receiver, an actuator element (2) arranged between the battery and the receiver and an alarm assembly (8) and further comprises, concealed along an outlet path (P₁--→P₂) to be covered by the bunch stolen by a robber to the exit of a bank, means for transmitting the electromagnetic waves, the actuator including a vibration switch (2) adapted to close a circuit on the battery (1) as it is vibrated by the displacement transmitted to the banknote bunch, the receiver being designed so as to actuate the alarm element exclusively if it receives from the transmitting means two different electromagnetic waves, offset from one another and suitably coded, each having a dedicated frequency f₁, f₂ and being received according to a given sequence.