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Study objectives Consumer sleep technologies (CSTs) enable low-burden longitudinal sleep monitoring, and their measures are often interpreted as equivalent to polysomnography (PSG) measures. We applied measurement reliability-aware approaches to determine whether CST-derived ‘sleep’ measures (1) are interchangeable or device-specific, (2) can reliably assess participant-level sleep characteristics and (3) converge onto interpretable principal components representing essential aspects of sleep. Methods Data from 74 older adults (20 people living with dementia) were collected at-home (total=752 paired nights) using four modalities simultaneously: research-grade actigraphy (Axivity), a wearable (Withings Watch), a nearable (Withings Sleep Analyser) and Sleep Diary, followed by one in-lab PSG assessment. We applied Bland-Altman analyses, repeated-measures correlation analyses, intraclass correlation coefficients (ICC) and principal component analysis (PCA). Results Single-night between-device correlations and correlations with PSG were weak (r