hey I have an idea
-the sapper can be launched (as it appears in the video he knows the spy)
-% 50 less damage to the sentinel
-% 20 more damage to the engineer to whom the sentinel belongs (I do not know how to explain it, for example the engineer is called david if your "hacking" your sentinel will give you a% 20 to david)

Pros:
When a sapped building is destroyed. It will deal explosive damage in a radius.

Cons:
Only 2 sappers can be deployed at a time (both will be used on teleporters if it has a connecting side)

Rather than a gadget that punishes engineers and pyros for doing their job as the item description would imply...

It would be something that punishes them for not being able to break the sapper more.

The sapper would have more of a beeping sound rather than a hissing sound so enemies will know that it's a bomb rather than the standard sapper.