Core77

Some interesting innovations in products (both aimed at kids) that help you complete a feedback-less task more effectively.

Squidsoap [via Strange New Products] is a pump that puts black ink on your hands when you pump out the soap; your hands are clean when they are free of ink (and happily, also free from invisible germs and gunk).

Listerine Agent CoolBlue is similar to good ol' Disclosing Tablets; it stains the placque on your teeth so you can see where you need to go back and brush.

Cleaning is a great category for this sort of thing; as we are more afraid of germs that we can't detect, we need some mechanism in our tasks to ensure that we're completing them properly. Consider vacuuming; one way to know you're done with the carpet is that you stop hearing the noise of dirt shooting past the rollers.