When using badblocks with the progress indicator on (-s option), the block number of the bad block(s) found is mixed in with the progress text, in the output of badblocks:
ubuntu@ubuntu:~$ sudo badblocks -s /dev/sda
Checking for bad blocks (read-only test): 40490816done, 14:29 elapsed
40490817done, 15:16 elapsed
40490818done, 15:39 elapsed
40490819done, 16:02 elapsed
I am still able to comprehend what the bad blocks are, but still I thought I'd point this out.