Develop new real-world evidence indicators of worsening and improving asthma. Scientists will measure (1) steps per day, (2) duration and intensity of exercise per day, (3) sleep duration and the number of awakenings per night using Fitbit activity trackers. Scientists will measure asthma symptoms using a once-monthly custom survey delivered to participant smartphones via Twilio. Scientists may measure rescue medication use and adherence to maintenance medications using digital inhaler devices. Scientists will correlate the above measures to participant-reported significant asthma exacerbations (SAEs), lung function (FEV1), and standardized surveys (i.e. the asthma control test (ACT) and global evaluation of treatment effectiveness (GETE)(4)) collected in clinic every 3 months. Coordinators will record any medication changes or reported medication side effects.

Determine response to omalizumab therapy. After participants are placed on omalizumab therapy as part of standard medical care, scientists will determine whether and how real-world evidence can be used to gauge responses to omalizumab. Then, scientists will determine which features, or combination of features, are the best indicators of disease control in the real world.

Inclusion Criteria:

• A diagnosis of uncontrolled or difficult-to-treat asthma, defined as 1 course of systemic corticosteroids (e.g. oral prednisone) in the last 12 months OR an asthma control test (ACT) score less than or equal to 19 despite regular use of inhaled corticosteroids (ICS) therapy (at least 176 mcg of fluticasone/day or the equivalent) for at least 1 month prior to enrollment.
• Participants will need access to a smartphone.

Exclusion Criteria:

• Active smoking and any significant comorbid conditions that could inadvertently interfere with study results as determined by the study investigators (i.e. any terminal illness, cancer, HIV, end-stage renal disease, congestive heart failure, severe autoimmune disease or inflammatory bowel disease)
• Conditions that require bursts of oral corticosteroids
• Other significant lung diseases (cystic fibrosis, pulmonary hypertension, interstitial lung disease, pulmonary fibrosis among others)
• Other disease that may mimic asthma, including vocal cord dysfunction, hypersensitivity pneumonitis, or tracheobronchomalacia.

Participants 18-85 years of age with moderate-to-severe asthma at the time of enrollment and eligible for omalizumab therapy.