Unfortunately Barcelona has a well-earned reputation for petty thievery – particularly pickpockets. Never carry a wallet in a back pocket. It may be helpful to distribute cash in different pockets. And keep handbags close at all times – never on the back of a chair.
Be aware that Barcelona’s notorious pickpockets target visitors, and public transport is a happy hunting ground, likewise busy tourist attractions (though you’re unlikely to be bothered inside attractions that charge fees).
Also be aware that these guys are professionals – it is all-too-easy to be scammed in one way or another.
If you do fall victim, you may need to make a police report. You can file a report online here, or in person at police stations, (the main one is at Carrer Nou de la Rambla, 76-78. Be prepared to wait; they have a lot of people to deal with). There is more info here for dealing with lost documentation.
You’ll save yourself some hassle if you have documented your credit card numbers, passport info, and phone IMEI number, and kept it safe elsewhere.
The emergency number is 112 to report robberies, accidents, assaults, fires, or medical emergencies.
Turisme de Barcelona offers a tourist information service at (+34) 932 853 834 daily from 8am until midnight, for tourists and visitors to answer any questions or help deal with incidents.