we spend 50 percent of our time on this site getting rid of snoop software, so it would be pretty hard for us to recommend some
Your question is...kind of curious....fist you want some, and then you want to know how to detect it, and can we point you to some free stuff.
So, I do not know how to reply--I am not sure if you really are the parent of a teenager or two or a teenager or two looking to circumvent a parent.
In either case, the best advice I can offer is to be a dilligent parent. If you have concerns, and you should, set boundaries. Place the computer in a public area and monitor the connection. Talk with your kids. Tell them your concerns. Treat them like adults
You may be surprised