Acceptance, operationalized as the users' degree of satisfaction with holly™ and quantified using the Client Satisfaction Questionnaire (CSQ-8), an 8-item measure with high coefficients of internal consistency reliability (Cronbach's alpha of 0.80 or greater) and adequate validity. The instrument will be modified to include a description of the holly™ "service". Total scores range from 8 to 32, with the higher number indicating greater satisfaction. Caregivers complete the measure following device usage.

To measure appropriateness, defined as the perceived fit, relevance, and compatibility of holly™ within the users' context, the investigators will be using an adapted version of the Barriers to Treatment Participation Scale, which demonstrates good psychometric properties regarding reliability and structure (internal consistency Cronbach's alpha of 0.85 or greater) and is reasonably valid. Caregivers complete this 32-item questionnaire rating of how much they agree with statements about their expectancies of barriers to treatment participation for their child, using a 5-point Likert scale (1=totally disagree, 5= totally agree). The total score ranges from 32 - 160, with higher score indicating greater barriers (i.e., worse outcome).

The investigators will measure the number of hours holly™ is worn during the three-week trial, and rate of change in usage from week 1 to week 3. This information will be recorded by hollyTM.

This measure will assess changes in sleep habits from pre- to post-device usage using the Children's Sleep Habit Questionnaire (CSHQ). Caregivers complete the CSHQ at enrollment (baseline) and again immediately after the device trial period. The CSHQ is a validated caregiver-reported measure of sleep behaviors in children, capturing domains such as bedtime resistance, sleep duration, night wakings, and daytime sleepiness. The total possible score ranges from 33-99, with higher score indicating worse outcome.

For participants who previously completed the CSHQ as part of the POND study at Holland Bloorview, existing data will be retrieved with participant consent (signed Release of Information) if collected within the last two years; otherwise, the measure will be repeated.

This measure will assess changes in emotion regulation abilities from pre- to post-device usage using the Emotion Dysregulation Inventory (EDI). Caregivers complete the EDI at enrollment (baseline) and again immediately after the device trial period. The EDI is a validated caregiver-reported measure designed to capture reactivity and dysregulation in children with neurodevelopmental conditions. The EDI uses a 5-point scale for items of problem severity over the past 7 days, where 0 = not at all a problem and 4 = very severe problem. It is scored on two subscales: Reactivity (intense emotional reactions) and Dysphoria (sadness, low motivation). Raw scores from the 24-item Reactivity scale (min = 0 and max = 96) or 6-item Dysphoria scale (min = 0 and max = 24) can be converted to t-scores for comparison against different population norms, such as a general youth sample or a clinical sample for individuals with autism. Higher scores indicate worse outcomes.

The Pediatric Quality of Life Inventory (PedsQL) will be used to evaluate changes in health-related quality of life from baseline to post-device usage. Caregivers will complete the age-appropriate version of the PedsQL (Young Child 5-7 years, Child 8-12 years, or Teen 13+ years) at enrollment and again immediately after the device trial period.

Each PedsQL form uses a 5-point response scale (0-4) that is converted to a 0-100 scale, with higher scores indicating better outcomes (i.e., better health-related quality of life). Subscale and total scores will be calculated according to standardized PedsQL scoring procedures.

This measure will assess changes in anxiety levels from pre- to post-device usage using the Parent Rated Anxiety Scale in ASD (PRAS-ASD). Caregivers complete the PRAS-ASD at enrollment (baseline) and again immediately after the device trial period. The PRAS-ASD is a validated caregiver-reported measure designed to capture anxiety symptoms specifically in autistic children. It is a 25-item, parent-report questionnaire where item is rated on a 0-3 scale, with a total raw score ranging from 0 to 75. Higher score indicates worse outcome.

The investigators will examine associations between phenotypic measures and neuroimaging profiles using existing structural MRI, diffusion tensor imaging, and resting-state data from the Province of Ontario Neurodevelopmental Disorders (POND) Network. With participant consent (signed Release of Information), neuroimaging data previously collected by the POND study will be retrieved when available.

This measure will summarize average heart rate recorded by the holly device during usage period. Heart rate data will be used to examine physiological arousal patterns over the trial period, along with other arousal variables, and to characterize changes across the trial period and to explore associations with phenotypic and neuroimaging profiles.

This measure will summarize heart rate variability (HRV) obtained from the holly device during usage periods. HRV will be analyzed as an indicator of autonomic arousal, along with other arousal variables, and used to characterize changes across the trial period and to explore associations with phenotypic and neuroimaging profiles.

This measure will record the count of physiological arousal events detected by the holly device during usage. Event counts will be evaluated over the trial period along with other arousal variables to characterize changes across the trial period and to explore associations with phenotypic and neuroimaging profiles.

This measure will summarize the average acceleration recorded by the holly device to summarize physiological arousal during device usage. Mean acceleration values, along with other arousal variables, will be used to characterize changes across the trial period and to explore associations with phenotypic and neuroimaging profiles.