Whoo boy. You asked a loaded question. We discussed this in depth a while back.

http://forums.teamestrogen.com/showt...ght=headphones

Quote Originally Posted by pooks
2) I can still hear everything around me, . . .
Regarding this comment which I hear frequently from people using earphones: How do you know you can hear everything? I haven't run a formal test and kept records but anecdotally I would say that 100% of earphone users that I pass on the road or bike path do not hear me coming. They do not hear me say (loudly), "On yer left" until I am shouting it in his or her ear while praying that they don't swerve into me. This includes runners and skaters. It also doesn't appear to matter whether it is one or both ear buds. Piece 'o cake to sneak up on these folks.

Since I am not intent on criminal activities, I just take the opportunity to make loud comments about them. They never hear me and it provides me a good giggle.