The Xiaomi Mi Band. If you're willing to wait, it can be had for less than $16 from China. Here's the Hot Deal thread about it:
http://forums.anandtech.com/showthread.php?t=2430522
I really like mine, if all you're worried about is the basics of steps/running tracking. It does this quite well. I much prefer it to my Fitbit flex. It's more comfortable to wear and the battery last an ungodly amount of time. I charged it when I got it 43 days ago and it's currently sitting at 22%. I don't use the alarm or phone notifications, so my battery life is probably extended beyond their listed 30 days (I find the vibration to be too weak to use the alarm).
I do use the secure unlock. The app doesn't think it's doing that as it's only really designed to work with one of their phones but the swipe to unlock is very convenient over the pin entry which my company's security software mandates. If I walk away from the phone and go out of bluetooth range I have to enter my pin to unlock.
Depending on how often you check the app, it can take anywhere from 30 seconds to almost instantly to update. Just pull down to force a refresh. There's been 2 app updates with firmware updates since I got it which is nice to know that it's actively supported for a cheap device.
I haven't noticed any real difference in the battery life on my S5.