Your pocket bomb doesn't have any actual bomb in it (unless the Israelis put some there, like the Hezbollah pagers and walkie-talkies.) They can burn fast, but afaik they don't explode, just like gunpowder doesn't explode. It burns very fast. On the other hand, they can produce gas and burst the battery pack, which might be considered an explosion, but I'd argue it's not actually one.

Which isn't going to make someone who has it happen in their pocket feel any better.

If I have my physics wrong, please correct me, I'm not a lithium bomb expert :)