Control method for an emergency device of a helicopter, said helicopter comprising a rotor adapted to be rotated, said emergency device being adapted to supply additional emergency propulsive power to the helicopter, said method comprising the following steps: - a step of measuring the rotation speed of the helicopter rotor, - a step of calculating the derivative of the measured rotation speed, - a step of detecting a drop in the rotation speed of the rotor at an instant to below the nominal rotation speed V NRnom of the helicopter rotor, - a step of activating a timer to measure the duration Δt from the instant t0, the timer being activated as long as the rotation speed of the rotor is dropping, - a step of measuring at an instant t0 + Δt the rotation speed of the rotor V NR, - a step of continuously verifying the following conditions: - the rotation speed of the rotor is greater than a predetermined value, said arming speed, - the derivative of the rotation speed is greater than a predetermined value, said arming derivative, - the derivative of the rotation speed at instant t0+Δt is lower than or equal to: V DEC − V NR dt - the derivative of the rotation speed at instant t0+Δt is greater than or equal to: V DEC − V NRnom Δt with V DEC being the stall speed of the helicopter rotor, below which the helicopter is in stall due to the loss of lift of the helicopter, - an activation step of the emergency device if the verified conditions are validated. - a step of measuring the rotation speed of the helicopter rotor, - a step of calculating the derivative of the measured rotation speed, - a step of detecting a drop in the rotation speed of the rotor at an instant to below the nominal rotation speed V NRnom of the helicopter rotor, - a step of activating a timer to measure the duration Δt from the instant t0, the timer being activated as long as the rotation speed of the rotor is dropping, - a step of measuring at an instant t0 + Δt the rotation speed of the rotor V NR, - a step of continuously verifying the following conditions: - the rotation speed of the rotor is greater than a predetermined value, said arming speed, - the derivative of the rotation speed is greater than a predetermined value, said arming derivative, - the derivative of the rotation speed at instant t0+Δt is lower than or equal to: V DEC − V NR dt - the derivative of the rotation speed at instant t0+Δt is greater than or equal to: V DEC − V NRnom Δt with V DEC being the stall speed of the helicopter rotor, below which the helicopter is in stall due to the loss of lift of the helicopter, - an activation step of the emergency device if the verified conditions are validated. - the rotation speed of the rotor is greater than a predetermined value, said arming speed, - the derivative of the rotation speed is greater than a predetermined value, said arming derivative, - the derivative of the rotation speed at instant t0+Δt is lower than or equal to: V DEC − V NR dt - the derivative of the rotation speed at instant t0+Δt is greater than or equal to: V DEC − V NRnom Δt with V DEC being the stall speed of the helicopter rotor, below which the helicopter is in stall due to the loss of lift of the helicopter, - an activation step of the emergency device if the verified conditions are validated.