So sadly, it has crossed my mind that I might be attacked on a run. I already gave you the option of stun guns and pepper spray on this post, but I found this and couldn't resist adding this to my list of 26.2 things to give to a runner.
It's a Spalding Electronic Whistle. Single tone electronic whistle that has a loud, consistent sound every time, even if user is short of breath or injured. Personal Safety & Signaling Device and includes 2 sets of AAA Batteries. It's also hand operated instead of mouth blown is sanitary, even for multi users. Get yours for $15.95 here.
Be safe out there!