No need to speculate, we can check if such situation indeed takes place in Switzerland.

Surveillance of employees is obviously banned anyway.

Yeah it is ridiculous to see all of the "employees" complain so heavily about one important work email that comes over the weekend, when the business patiently puts up with hundreds of personal phone calls, time spent scrolling on the phone, hacker News / Reddit posts and much more.

There needs to be a little bit more of a give and take. If employees are not expected to receive a single phone call or email outside of working hours. Would it be acceptable if the same restrictions were placed on personal calls and emails during working hours?

How many of the same people would be screaming murder, if their bosses came to them and complained about them taking personal email during work time.