I don't have the Pro Version installed but I'm able to remotely lock my device from the AVG site. Absolutely free :) No fees whatsoever

AVG should do the job. I've been having the S4 for over a year now and used Avast and Lookout also but AVG is still my favorite. Especially the remote admin feature that allows you to locate or lock your device when its lost. I tested it just to see how it works and its great. Location more precise than Lookout. Avast just looks too busy for me :laugh: