If you touch someone or talk to them, the spell will wear off.
Is that not a bit like saying "Here is a spell to heal a cold, but you must also take cold medicines, if you dont then the spell will wear off?"
Presumably the answer to my question is something along the lines of "no spell can make you invisible to other people or make them not notice you if you are obvious about your actions" in which case my response is "well then your spell isnt very effective, i can quite easily blend in with my surroundings by not being provocative, the human mind is adept at filtering information and if i am not important to the brain it will ignore me. It isnt the spell which makes you unnoticed it is your body language and actions."
No spell can make you invisible, either truly or as in this case simply unnoticed. It is a falsity.