Inclusion Criteria - Alpha and Beta Phase B1
- Age 18 years or older, able to comply with all study procedures and capable of providing informed consent.
- Mentally competent to understand and able to perform written, informed consent to participate in the study
- A diagnosis of either ET or PD as determined by clinical history
- Moderate to severe upper limb tremor
Exclusion Criteria - Alpha and Beta Phase B1
- Pregnant women
- Swollen, infected, inflamed areas, or skin eruptions, open wounds, or cancerous lesions of skin at stimulation site
- History of psoriasis, eczema or atopic dermatitis at the stimulation site
- History of peripheral neuropathy in the upper limbs, including carpal tunnel syndrome and diabetic neuropathy
- Participant unable to communicate with sponsor/investigator and staff
- Any other medical conditions or physical or mental impairments that in the sponsor/investigator's opinion would render the subject unsuitable as a candidate for the study.
Inclusion Criteria - Beta Phase B2
- Age 18 years or older, able to comply with all study procedures and capable of providing informed consent
- Mentally competent to understand and able to perform written, informed consent to participate in the study
- For ET subjects, a diagnosis of essential tremor defined as definite or probable ET based on TRIG criteria
- For PD subjects, a diagnosis of Parkinson's disease by a Movement Disorder Specialist
- For ET subjects, at least one hand exhibiting tremor > 2 as assessed by the Essential Tremor Rating Assessment Scale (TETRAS) finger to nose task, duck wing task, OR Archimedes Spiral completed during the Screening visit
- For PD subjects, a score > 2 on at least one of MDS-UPDRS items 3.15, 3.16 or 3.17 At the Screening Visit, a score of > 3 on one of the following subject-assessed items of the Bain \& Findley Activities of Daily Living Scale (BF-ADL): Use a spoon to drink soup, Hold a cup of tea, Do up buttons, Do up a zipper, Write a letter
- Stable medications for at least 30 days prior to enrollment and the ability to maintain tremor medications throughout the duration of study participation
- For PD subjects, able to participate in visits in a practically defined OFF state (withdrawal from all tremor medication for 12 hours prior to study visits)
- A wrist circumference of 6.0 - 8.1 inches
Exclusion Criteria - Beta Phase B2
- Pregnant women
- Swollen, infected, inflamed areas, or skin eruptions, open wounds, or cancerous lesions of skin at stimulation site
- History of psoriasis, eczema or atopic dermatitis at the stimulation site
- History of peripheral neuropathy in the upper limbs, including carpal tunnel syndrome and -diabetic neuropathy
- Participant unable to communicate with sponsor/investigator and staff
- Any other medical conditions or physical or mental impairments that in the sponsor/investigator's opinion would render the subject unsuitable as a candidate for the study