Inclusion Criteria:

• Able to give a written Informed Consent Form.
• Patient who is willing to comply with study restrictions including E4® device management (wearing and charging the device) and Femme Rhythm Patient App Management (pairing E4® device and the patient Femme Rhythm App, and carrying the smartphone for answering questionnaires and data reporting).
• Female patients aged ≥ 21 and < 50 years.
• Patient who meets either A or B or both in the following criteria:
  • Confirmed diagnosis of endometriosis (laparoscopy/laparotomy) performed WITHIN 10 YEARS prior to the study participation;
  • Current clinical diagnosis (endometriotic cysts or deep infiltrating endometriosis detected by TVUS, TRUS or MRI) WITHIN 6 MONTHS prior to the study participation.
• Patient who meets either A or B in the following criteria:
  • Patient is NOT treated with hormonal agents for endometriosis WITHIN 4 WEEKS prior to study participation, and have reqular menses (i.e., 21-38 days) within 38 days prior to the study participation;
  • Patient started hormonal agents for endometriosis, including combined oral contraceptives MORE THAN 8 WEEKS prior to the study participation, or progestins, danazol, GnRH agonists, GnRH antagonists or Progesterone and Levonorgestrel Releasing IUDs MORE THAN 12 WEEKS prior to the study participation, AND stable use of the medication is expected during the study period 6. Patient has a moderate to severe endometriosis associated pelvic pain using the Monthly Assessment of Endometriosis Pain within 28 days prior to study participation.

Exclusion Criteria:

• Patient is pregnant, or breast feeding or is planning a pregnancy during participation of the study or is less than 6 months postpartum, post-abortion, or post-pregnancy before participation.
• Patient has chronic pelvic pain that is not caused by endometriosis that requires chronic analgesic or other chronic therapy, or that would interfere with the assessment of endometriosis related pain (e.g., pelvic inflammatory disease).
• Patient has more than five surgical histories in pelvic area.
• Patient has a skin disease or condition that would interfere with the collection or interpretation of physiological data obtained through E4®
• Patient required neuromodulator (a long-acting or immediate release narcotic, or gabapentin) during 3 months prior to the study participation.
• Patient has a planned surgery during the study.
• Patient had a surgery within 4 weeks prior to the study participation.
• Patient has a planned trip overseas during the study participation.
• Any other reason that, in the judgment of the investigator, would render the subject unsuitable for the study participation.