With VoiceUtils can add custom commands to Siri number with which you can do a fast respring, reboot your iPhone, turn it off, or put it in Safe Mode. The only flaw I have is that Siri's voice cuts to begin the action, but it works well to make a fast respring.
4S Compatible with iPhone, iPhone 4, 3G and any device with Spire (Siri) installed.
You can download it for free on Cydia.
The'll find BigBoss repo.
You need to have done the jailbreak.