Could a smartphone app and two sensors prevent tension headaches?

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * 18 years of age inclusive or older, at the time of signing the informed consent. * A diagnosis of TTH according to the criteria of the International Classification of Headache Disorders 3rd edition (ICHD-3) * History of at least 6 days or more with TTH per 28-day period in the 3 months prior to screening (as recalled by the subject). * Frequency of at least 6 days or more with TTH per 28-day period, confirmed by daily diary entries in the baseline period. * At least three months of experience with smartphone and access to an iOS or Android phone at home. * Capability of giving signed informed consent which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in this protocol. * Onset of TTH (and migraine, if present) before the age of 50 years. * The onset of TTH should be present for at least 1 year prior to inclusion. Exclusion Criteria: * Subject does not master a Scandinavian language at a level sufficient to fully understand the written and verbal study information. * Subject is unable to differentiate TTH from other concomitant headaches. * A history of more than 1 migraine attack per month on average in the last year, as recalled by the patient. * Frequency of more than 1 migraine attack per month during the baseline period, as confirmed by daily diary entries. * Subjects diagnosed with trigeminal autonomic cephalalgias and cranial neuralgias. * Subjects with secondary headache conditions with the exception of medication overuse headache (MOH) as defined in the ICHD-3 criteria that undergo a successful 8 weeks acute medication stop, and does not overuse medication in the following 28 day period. * Use of concurrent TTH preventive medication, with the exception of stable dose (≥3 months or 5 half-lives, whichever is longer) monotherapy of TTH preventive medication. * Use of prophylactic medication with known prophylactic effect on other headache disorders, whatever the indication, with the exception of stable dose (≥3 months or 5 half-lives, whichever is longer) monotherapy of any preventive medication. * Subjects taking opioids (\>3 days per month) or barbiturates at the time of screening. * Reduced sensibility, hearing or vision to a degree that impairs proper use of the app. * Patients with comorbid psychiatric disorders with psychotic or other symptoms making compliance with the study protocol difficult, at the discretion of the investigator. * Patients exhibiting a high degree of comorbidity and/or frailty associated with reduced life expectancy or high likelihood of hospitalization, at the discretion of the investigator. * Use of non-pharmacological preventive treatment, that in the opinion of the investigator is likely to interfere with the evaluation of the biofeedback treatment strategy under investigation. Stable non-pharmacological treatments for other indications than TTH that is not likely to interfere, is allowed if it is kept unaltered during study participation. * Previous or current use of biofeedback equipment. * Other pain conditions, not intended to be treated in this study, that in the opinion of the investigator could interfere with study procedures, accurate pain reporting, and/or confound evaluation of study endpoints * High probability neurological deterioration due to other medical conditions, that in the opinion of the investigator may confound outcome assessment. * Have within 6 months of enrolment a significant untreated addiction to dependency-producing medications, alcohol, or illicit drugs. * Abnormal pain behaviour, inappropriate medication-use and/or unresolved psychiatric illness, that in the opinion of the investigator are significant enough to impact perception of pain, compliance with intervention and/or ability to evaluate treatment outcome. * Subject is currently participating or planning to participate in another clinical investigation. * Subject who is unlikely to follow Clinical Investigation Plan or where treatment seems futile in the opinion of the Investigator or have demonstrated an inability to sufficiently adhere to headache diary entries (\<70%). This study excludes patients with more than 1 migraine attack per month. A migraine attack is defined according to ICHD-3 criteria as attacks of unilateral, pulsating, moderate or severe headache lasting 4-72 hours that is aggravated by physical activity, associated with nausea and/or photophobia and phonophobia, and, in some cases, preceded by unilateral, fully-reversible central nervous system symptoms.