The benefits of physical activity and adequate sleep are well documented, and their importance strengthens with the increasing prevalence of chronic diseases and multimorbidity. Interventions to promote physical activity and sleep that use commercial activity trackers may be useful non-pharmacological approaches to managing individual health; however, limited evidence exists on their use to improve physical activity in elderly patients with multimorbidity. This study aims to measure the effects of behavioral change techniques (BCTs) delivered by a wearable device on physical activity (PA) and quality of sleep (QS) in elderly patients with multimorbidity. The investigators designed an open-label randomized controlled trial with participants recruited through primary care and a specialist outpatient clinic. Participants must be more than 65 years old, have multimorbidity, and have access to smartphones. All eligible participants will receive PA promotion content and will be randomly assigned to wear a smartwatch. The primary outcome will be the participants' PA measurement at six months using the IPAQ-SF. Secondary outcomes will include changes in the participants' frailty status, biometric measurements, quality of life, and biopsychosocial assessments. A sample size of 40 participants per arm was calculated to detect group differences, with 50 participants recruited and randomized into each arm. This study aims to contribute to a better understanding of PA patterns and the impact of smartwatch-based PA interventions in patients with multimorbidity. The trial's findings are expected to improve our understanding of how physical activity patterns, patient-reported outcomes (PROMs), and healthcare resource utilization are linked in patients with multiple medical conditions. The study will use a registry for locally developed PROMs and data from the participants' medical records to determine how wearable data and medical information data can be used to predict PROMs and unplanned hospital admissions.

Inclusion Criteria:

• Multimorbidity defined as the presence of two or more of the following chronic conditions: hypertension, depression or anxiety, chronic musculoskeletal conditions causing pain or limitation, arthritis and/or rheumatoid arthritis, osteoporosis, asthma, COPD, ischemic heart disease, peripheral artery disease, heart failure, cerebrovascular diseases, chronic stomach or colon conditions, chronic hepatitis, diabetes mellitus, thyroid disorders, any active cancer in the previous five years, chronic kidney disease, chronic urinary conditions, hyperlipidemia, and obesity
• Must have access to their smartphones

Exclusion Criteria:

• patients who are sufficiently physically active (IPAQ-SF > 150 min aerobic physical activity per week)
• existing absolute contraindication for PA according to the American College of Sports Medicine (acute myocardial infarction within two days, ongoing unstable angina, uncontrolled cardiac arrhythmia with hemodynamic compromise, active endocarditis, symptomatic severe aortic stenosis, decompensated heart failure, acute pulmonary embolism, pulmonary infarction, deep venous thrombosis, acute myocarditis or pericarditis, acute aortic dissection, physical disability that precludes safe and adequate testing)
• poor comprehension of Portuguese language
• disabling neurological disorder (defined as mRankin score ≥4), severe psychiatric illness, learning disability, dementia and cognitive impairment, registered blind
• housebound or resident in a nursing home or non-ambulant
• advanced cancer
• scheduled for surgery within five months after the first consultation
• orthopedic or rheumatologic diseases with severe impairment
• chronic pain syndromes with inherently reduced mobility

The masking procedure will involve blinding the outcome assessors to the treatment allocation of the patients. This means that the outcome assessors will be kept unaware of whether the patients are wearing the device or not.