Android: how to handle backpress when activity from another application is started to get the result?

Android: how to handle backpress when activity from another application is
started to get the result?

I'm developing an financial application that require finger-print for
transaction. My target device has a built-in finger-print scanner and an
application that returns the captured fingerprint.
In my application, I'm starting that application when the finger-print is
required. And the captured finger-print is passed to the server by calling
a web-service. The finger-print application has a button named "Return
with Fingerprint" that returned the captured finger-print to its caller as
byte. So if any user gives his fingerprint and presses that button, the
fingerprint app finishes and returns to my app. But the problem is, if the
user pressed backbutton when he is on the finger-print application, the
system doesn't return to my app, rather it goes to "Android Home" and I
need to reopen my application.
I want to control the backpress when I have called the fingerprint
application using startactivityforresult(fingerprintApp)