Should have seen this one coming, really.
For several years now I've been considered by Social Services to need help in the mornings, to get properly and safely washed, dressed, medicated and generally ready to face the day. We only took it up a few months ago (whole other story), and it has been working well and has made a very welcome difference to my life.
This morning my assistant arrived and rang the doorbell - some people have key safes but since I can usually get to the door one way or the other, we've chosen not to have one. Normally that's fine, but today, the Roomba was running. I did not hear the doorbell. I did not hear the doorbell again. I did not hear the knock on the door or the call through the letterbox. The blinds were all shut (unsurprisingly as I was not yet dressed). The poor woman ended up basically running around the house knocking on all the windows with increasing panic. Eventually she reached the one by which I was sitting, but by the time I'd levered myself up to crack the blinds and see who was knocking, she'd already run back round to the front of the house and was about to call base and ask them to ring me... she was extremely relieved when I opened the door.
We've decided that while the Roomba is a wonderful thing, it's best not run when I'm expecting my care calls.