An intraoral aversion device to assist a user in quitting an undesirable behavior such as tobacco smoking, tobacco chewing, use of snuff, illicit drug use, excessive alcohol consumption, excessive food consumption, and/or other undesirable activity facilitated via the mouth. The aversion device may be wholly or partially configured to be disposed in the user's mouth, for example. The aversion device may include a detector and a output device, wherein the detector is configured to detect a parameter indicative of the user engaging in the habit or undesirable activity. If (and only if) the detector detects such a parameter, the output device delivers a negative stimulus to the user, thus providing negative feedback and creating an incentive for the user to limit if not eliminate the undesirable activity.