This app will detect incoming encrypted messages and fire a notification. You can decrypt messages either directly from your SMS inbox or from the clipboard.
The current supported cryptographic algorithms are:
Morse Code (very weak)
Rail-Fence (very weak)
Rot-13 (very weeak)
AES (very strong)
One Time Pad (Mathematically Unbreakable)
Update: Unbreakable SMS (PAID) is now free! Funny story, that - I forgot my password and couldn't issue updates to the old version anymore. Instead of making everyone buy it again, I decided to just release a free version with all of the same features as the original, plus a few extras.