The Invisibility Ray is an invention of Doofenshmirtz.
Doofenshmirtz showed Perry the Invisinator, a ray that could cause objects to become invisible, which he planned to use on the Fireside Girls when they came to sell him cupcakes or raffle tickets. He told Perry that he was annoyed that when he left his shades up, they could see that he was home, so he couldn't just ignore them and pretend he wasn't home, and they would make big pleading eyes that make him feel guilty, so, rather than shooting himself with the ray so they don't see him, he decides to shoot the girls with it so that he wouldn't have to look at them.
Perry began to file at the bars of his cage with an invisible file, so Doofenshmirtz was driven to release his invisible tiger, but instead of attacking Perry, it attacked Doofenshmirtz. He managed to drive the tiger back through the trapdoor, and closed the door. But Perry, it seemed, had already escaped. Perry, swinging on a rope, kicked Doofenshmirtz. Doofenshmirtz rolled through the invisibility ray, leaving him completely invisible. Doofenshmirtz thought Perry would be unable to find him, and didn't refrain from telling Perry so. This, however, allowed Perry to locate him, and Perry gave him a series of kicks and punches, making him to roll back through the invisibility ray, which him to become visible again. Doofenshmirtz remarked that he didn't know that it could do so. Perry then threw a chair through the ray, at Doofenshmirtz.
- Doofenshmirtz's plan was to use it on the Fireside Girls when they try to sell him cookies.