It depends on the power of the dismount. Descending off the horse smoothly should not cause the airbag to deploy. However, if you jump off your horse, the system may deploy.
Helite’s airbag systems contain a mechanical system that prevents unexpected activation. The tractive force required to trigger the airbag is between 20 and 30kg depending on the size. If the rider forgets to detach themselves when getting off the horse, they will feel a strong tension on their garment.
Similarly to the seatbelt in a car, attaching and detaching the lanyard will quickly become a habit.