Your flight attendant wishes you happy birthday. Is that cute or creepy?

Airlines know a lot about you, from date of birth and home address to travel patterns, vacation preferences, beverage purchases and whether your last flight was good or bad. Now the latest generation of hand-held devices used by flight crews has an overhead bin full of information about each passenger.

Carriers are using it in an effort to improve customer service. They can congratulate customers on reaching 3 million lifetime miles or toast a couple’s wedding anniversary. At some airlines, they can tell if you really paid extra for that extra-legroom seat or are traveling on a restricted basic economy ticket. Someday soon it may be, “Having the usual vodka tonic tonight, Scott?”

Right now, airlines are trying to figure out when personalized interactions could be considered invasive, amid growing concerns about how companies like Facebook and others are using personal data. While many travelers are pleased to see their loyalty acknowledged, they’d all rather have upgrades. And plenty of others prefer a bit of anonymity once they get on an airplane and leave town.

United rolled out a new app to its flight attendants earlier this year with so much information about people, the airline has been reluctant to turn on all the functionality. The tool can show flight attendants information on each frequent flier’s five previous flights—green if it was a good flight, yellow or red if something went wrong, like a delay. But United is worried some customers might consider that stalking.