I message my wife when I get to work and when I’m leaving. So somewhere between an hour and 7 or 8 depending on exactly when in my day I get nabbed for her to notice.
My work colleagues would probably try to call me if I didn’t turn up (I’ve fallen off my bike before so they might suspect that) but I don’t think they would put out a police report immediately if I just didn’t turn up one morning.
UK resident: pretty sure you can’t dictate to your employees what they do on non work time unless you pay them on call wages. Ie be here and wear this. I guess you could write it into the contract and see if someone signs it but I don’t think it would hold up.