Regarding yichud with non-persons:
I once worked at a job at which I was allowed to choose my own hours according to my convenience. This arrangement worked really well for me since I was allowed to go to work and leave whenever I felt like it.
There was only one man who worked there besides the boss. One day, he told me that he lost his key so he wanted to know what hours I was going to be there since he didn’t have a key to get in or lock out so he could only work when someone else was there, and I was the only one who ever worked in the evenings.
I had asked a sheilah about yichud and was told it was no problem since there were other people in the building and since anyone could enter at any time. But it was annoying for me to have to decide exactly when I was going to be working. The reason I liked the job was precisely because I could work when I felt like it.
However, since it was a one-time thing, I didn’t make a big deal out of it. But then he kept asking me every day to let him know when I’d be working. I couldn’t deal with that, so I asked him why he didn’t just ask for a new key. He said his Rav had told him he’s not allowed to have the yichud with the computer, so that’s why he didn’t have a key.
I told this story to someone and he thought it was funny that “yichud” with a woman was okay but not with a computer. I also thought it sounded funny, but I also thought it made sense.
The differences are:
1. It’s easier to be machshil with a computer, because you can convince yourself that it’s not a “real” aveira.
2. With another person, both people have to be nechshol.
3. People are embarrassed to do something wrong in front of other people.
4. It wasn’t yichud for me because someone could come in at any time. With a computer, it’s easy to quickly shut it off when you hear/see someone coming.
That being said, I don’t think anyone would say there’s a yichud problem with a clock. And I don’t think you have to be a rabbi for that “psak”.