OkSiri, a recent addition to the Cydia Store, allows jailbreakers to have their favorite personal assistant listen out for its user's call. You can download the Android-inspired package free of charge on the Cydia Store, and it's optimized for iOS 7 and ARM64-devices.
Borrowing from Android's “Okay Google” functionality, OkSiri actually works alongside Activator in order to port the feature over to iOS. Both packages can be downloaded for free; once installed, users will need to assign an action to OkSiri, and performing this action will have OkSiri listen out for a preconfigured keyword.
Naturally, one likely keyword for the package would be “Okay Siri,” though a text field allows users to set anything they like. “Oy, Siri!” and “Wake up” are both viable alternatives; from here, speaking your chosen keyword should have Siri activate.
Ryan Petrich's (@rpetrich) Activator is definitely a package worth installing on your iPhone, even if you don't plan on taking advantage of OkSiri. The jailbreak tweak allows users to set actions to gestures from inside of a dedicated iOS app, and a growing number of other packages (including Knock and App Activate Pro) have expanded on Activator's already-impressive feature set in a number of different ways.
As mentioned, OkSiri can be downloaded on the Cydia Store free of charge.
See also: KakaoTalk Launches Official Mac App, Debuts New 'Search Chat' Feature, Report: Microsoft's Own Smart Watch Will Sync With iOS Devices, and Anti-Google Search Engine Alternative DuckDuckGo Updates Official iOS App.