To assess the ability of a machine learning algorithm to accurately detect fussing and crying time in infants using accelerometery data collected from a wearable device, compared to the Barr's parent-/caregiver-completed behaviour diary.

Inclusion Criteria:

1. Aged between 4-12 weeks at screening.
2. Gestational age 37 weeks - 41 weeks at birth.
3. Birth weight appropriate for gestational age (AGA - weight between 10th and 90th percentile) or Large for Gestational Age (LGA - weight above the 90th percentile) determined using WHO Weight-for Age percentile guides.
4. Infant has excessive crying, defined as 3 or more hours per day, during 3 or more days in the preceding week.
5. No birth trauma and nonsyndromic.
6. Readiness and the opportunity for parents/caregivers to fill out a study diary, questionnaires and for infant to wear device.
7. Parent/caregiver with ability to understand and comply with the requirements of the study, as judged by the Investigator.
8. Parent/caregiver willing and able to give informed consent for their and their infant's participation in the study.
9. Infant is considered healthy, following physical exam.

Exclusion Criteria:

1. Infants with failure to thrive, intrauterine growth retardation, haematochezia (blood in the stools), diarrhoea (watery stools that takes the shape of a container > 12x in breastfed and >5 in partially breastfed infants daily), or fever (38.0 degrees).
2. Premature infants (<35 weeks gestation at birth).
3. Infants with congenital heart disease, immunodeficiency, asplenia, cancer, cystic fibrosis, formula-fed infants, and those with liver disease.