At my current job - a UK-based development company - I set a vibrate-only alarm on my phone that goes off for only a second at 5:30 pm (which is my official end time). I don't like to literally watch the clock as it would be distracting and unprofessional.
I have this alarm set so I am on time to catch a train which only comes every 45 minutes.
If anyone heard my alarm, it would be like I had just gotten a text or email alert. The only person who could hear it was my supervisor, who quickly realised its regularity. In a recent employee review, my supervisor criticised the use of this alarm because it made me 'seem too regimented' and 'it was as if I was not enjoying my time at work'. He is aware of my travel circumstances and I have never expressed a dislike of my work. I asked if anyone else had noticed it or was bothered by it, to which he said no. I was not told to stop setting the alarm but I have done so for now anyway.
I always arrive well before my contracted start time. I have almost never had to work overtime because of a missed deadline, though I have on a couple of occasions demonstrated that if an urgent situation arises, or if someone approaches me, at 5:29 pm, I will stick around until it is safely resolved.
In an environment where people contractually finish at various times / use flexible working hours, is it still unprofessional to have a personal alert for your own finishing time?