I have both, an Ampera and a Zappi. the following occurs:-
Use Zappi as a dumb charge point (fast setting) and the car's timers. Works perfectly.
Use any timer function on the Zappi and the car sounds the horn as it switches on - this is the plug in honk.
Eco mode as it draws from the grid when needed at least only honks as you plug in (do not use the Zappi timers).
Using the ECO+ mode where the Zappi turns On and Off the car as the solar power is available - each time it switches on the car honks... Great for the neighbours
@HandyAndy has a defeat for the horn sounding so you could use the Zappi.
Interesting - if you turn down the Zappi to 10/11 amps in the menu then the Ampera thinks its a granny lead and in MY13 cars enables the charge selection menu and defaults to 6 Amps as it does with a granny lead.
Why do I have one, well the chance to get one at 5% VAT when the Solar went in and for use with the next car. It's also a well made box with decent safety functions.
NOTE: a tethered version is probably a bad idea as you will need to change the type1 tether for a type 2 one with the next car. Mine is untethered for this reason.