Any "trick" to use some keys to launch an application?

Question

Hello,

I am currently developing an free application (TaskOS ) that allow users to have multitasking and switch easily between applications on their mobile ( like alt+tab in Windows )

That work pretty well and user can launch my application by a long press on the "search" button" by adding this line in the manifest:

<action android:name="android.intent.action.SEARCH_LONG_PRESS" /> 

I also succeed to allow to the users to Use the camera button ( they can of course disable that in application settings) and the way to do that is slighlty different:

 <receiver android:name=".CameraPressed"> 
<intent-filter  android:priority="10000"> 
<action android:name="android.intent.action.CAMERA_BUTTON"/> 
</intent-filter> 

I am now wondering if there are other ways to launch easily my task switcher?

( long press on Home key, long press on trackball, or any other idea.)

Reading the Google documentation does not help me a lot.

Any other idea/suggestion would be warmly welcome.

Christophe