For some time now all properties here have had to acquire guest details and forward them to the local Mossos (Police), as a means of regulating both the property and guests visiting the country, or moving within the country.
To do this I use a handy little app called Check in Scan, with which I can scan the barcode on ID cards (For the EU) and passports, capturing all the necessary information in one go.
This information is then sent electronically to the Mossos. Before this information had to be collected manually and taken by hand to the Mossos Commisaria (Police Station). Thank goodness for technology for making life easier.
And don't worry about your information. It is a secure system and no details are stored by us.