I don't think it's unreasonable to want a quick text at all. My wife always texts me if she's spending the night at her boyfriend's house, or if she's coming home late, and ever if I know she's spending the night she usually sends me a quick goodnight text, it's just a small gesture to show that she cares and it makes a difference to me. If all you want is a quick text, that takes what, 15 seconds? There are always times when you're spending the day with someone when you have time for a text.
I agree with other on here who said you have the right to ask, and I don't think what you're asking for is unreasonable at all, in fact I think it's pretty darn reasonable.