Safe to open old sony remote?
You could have a leaky battery; you don't want acid all over your skin. There will be trace amounts of the heavy metals found in all electronics manufacturing. 

And because remotes are handled so much and are often full of skin cells and food traces, you could be smelling mold spores. 

Wear gloves, ventilate, and proceed. You should be fine as long as you don't lick anything!