what was one thing in the invelope ron sent to harry on his birthday?

It is a Sneakascope, a magical device which flashes and spins if there is someone untrustworthy in the immediate area.

"- this is a Pocket Sneakoscope. If there's someone untrustworthy around, it's supposed to light up and spin. Bill says it's rubbish sold for wizard tourists and isn't reliable, because it kept lighting up at dinner last night. But he didn't realise Fred and George had put beetles in his soup."