Short and Long-term Responses of PD Symptoms to Earstim

Inclusion Criteria: Patients fulfilling the following criteria are eligible for participation: * Subject must be ≥44 years of age. * Subject has PD and is on stable carbidopa/levodopa therapy for at least four weeks prior to enrollment in the study. * Subject must be willing and able to refrain from changing PD medications or dosages during the 90-day study. * Subject reports experiencing both "ON" and "OFF" episodes (MDS-UPDRS Part IV - Time Spent in the OFF-state score ≥1), as assessed and determined by the investigator. \*This corresponds to item 4.3 in MDS-UPDRS Part IV, where a score of 0 (zero) indicates that the subject experiences no OFF periods during the waking day, and a score of ≥1 reflects the presence of OFF periods at any level. * Subject experiences "OFF" periods with an "ON" score that is ≥20% better than the "OFF" score, as measured by the MDS-UPDRS Part III score, 1 hour after taking their dose of carbidopa/levodopa. * Subject has an MDS-UPDRS Part III score ≥33 in "OFF" period. * Subject agrees to remain in an "OFF" period for up to 3 hours without requiring rescue medication. * Subject can walk independently, without the use of an assisted device (e.g., cane or walker), in both "ON" and "OFF" periods. * Subject is willing to provide informed consent to participate in the study. * Subject is willing and able to comply with all study procedures and required availability for study visits. Exclusion Criteria: Patients who meet any of the following criteria are to be excluded from participation: * Subject has a medical or psychiatric comorbidity that may compromise participation in the study. * Subject has a history of cardiac rhythm disorders (e.g., atrial fibrillation, ventricular tachycardia, or atrioventricular block). * Subject is pregnant or planning to become pregnant during the course of the study. * Subject has a form of Parkinsonism other than PD, such as drug-induced Parkinsonism or Multiple System Atrophy. * Subject is currently using on-demand medications for PD, such as subcutaneous apomorphine, sublingual apomorphine, and levodopa inhalation powder. * Subject has an implanted deep brain stimulator (DBS). * Subject is receiving direct intestinal infusions of levodopa. * Subject has a history of epilepsy. * Subject's medications are expected to change during the 90-day study period. * Subject has a cardiac pacemaker, defibrillator, bladder stimulator, spinal cord stimulator, or any other active electronic medical device. * Subject is unable to understand or follow the instructions required by the study. * Subject has an ear infection or skin condition around the ear. * Subject is participating, or has participated, in another interventional clinical trial in the last 30 days that may confound the results of this study, unless approved by the Sponsor. * Subject has a history of brain surgery or peripheral neuropathy. * Subject is actively using TENS or has a history of chronic TENS use within the last 2 weeks prior to study enrollment. * Subject consumed alcohol or caffeine within 12 hours of study enrollment or has a history of alcohol dependence