The YesDear 5000, or Boyfriend Helmet, is a helmet Lizzie used to get Nigie to spend time with her instead of hanging with his friends. It was later modified by James Nixon McGarfield to be used on Lizzie.
The YesDear 5000 works by controlling the mind of the man wearing it, making them unquestionably obedient to the woman controlling it, though not without severe pain. The helmet is controlled via remote control, and the severity of its effects can be increased or decreased accordingly. If the helmet is on the head of a mind-controlled person too long, it fuses to the victim, leaving them brainwashed forever.
While powerful, the helmet can be disabled if the person wearing it is stressed to the point of creating enough feedback to destroy it, although this is very uncommon.
Lizzie grew annoyed at Nigel spending more time with his friends than with her, so she ordered a "YesDear 5000" from a magazine to control him. She gifted it to him as an apology and through guilt made him put it on. Once the helmet was strapped on, Lizzie made him ditch his friends to go be with her. Numbuh 2 and 4 later mentioned it to Numbuh 3 and 5, who immediately recognized it to be a "Boyfriend Helmet", and they set out to rescue their leader. Nigel was too strong to be taken down by his teammates, but the rage Nigel got from seeing the restaurant bill was too much for the helmet to handle, and it broke off (Operation: L.I.Z.Z.I.E.).
Jimmy Nixon McGarfield obtained and modified one helmet so that it would work on girls and make Lizzie his "bride" during a big snow day. He had her kidnapped and put under the control of the helmet, but Numbuh 1 made it malfunction by spilling soup on it (Operation: S.N.O.W.I.N.G.).