I've ordered a pair of 5.5mm x 1.7mm plugs to see if that would work. It's a bit awkward to measure the pin on the socket but it looks like it might be about right. The site calls them "Jack" plugs (which I always thought they were) but when I previously mentioned that to a house-alarm person he told me they weren't called "Jack plugs" and they had a special name (which I've long forgotten).
Anyway, I shall report back in case it helps other Aurora owners.
Thanks all.
Kind regards.
From Mike.