Other times it’s appropriate to use the non-emergency number is for nuisance calls. A barking dog or an illegally parked car are things that are annoying (and violate certain ordinances), but are not life threatening. If you cannot find your car, that is not necessarily an emergency. If you saw someone physically steal it then yes, call 9-1-1 immediately. Otherwise you can find out if it’s been towed or file a stolen vehicle report through the non-emergency number.
PRO TIP: The Arlington County Police has a great system in place for making online reports. Once the report is submitted, you will automatically receive a temporary case number. You will then receive an e-mail from an officer within 48 hours to follow up. If further information is needed, the Officer will ask for it via e-mail.