So I called the RTA yesterday about getting an eTag. I don't know Sydney roads that well so I was asking about what roads had what toll etc and also how sensitive the sensors are i.e. where i should mount the tag I got to the subject of the harbour bridge and the way there are boom gates. I asked if i had the tag mounted somewhere i couldnt easily remove it and it failed to open the gates. the guy said "er...well then you're screwed" ! ps if anyone has any tag advice i'm more than willing to listen!