I did not know about the rule to honk before turning but in the old days, as far as I know, one could use your right arm/hand when turning.
I am not sure if it´s allowed nowadays but in a similar manner I wonder if an electric horn can be substituted by the driver screaming loudly and if there is a Satnav beside you ask her to scream as well.
If this would be accepted by the authorities I would have had no problem with my horn push :-)
// Hakanplus8 from Sweden
