OkSiri is an iOS jailbreak tweak that enables always-on keyword listening (similar to the "OK google" feature on the Moto X or the "hey Siri" feature coming in iOS 8).
Stable version available on BigBoss repo here: http://moreinfo.thebigboss.org/moreinfo/depiction.php?file=oksiriDp
You can also add my beta repo to Cydia: http://jzplusplus.github.io/
WARNING: beta version has known issues.
Licensed under GPL v2.