KnowYourPrime Evidence Registry · Finding KYP-ER-0021

Cuffless Blood Pressure Accuracy at Night

Question assessedCan a cuffless smartwatch, bracelet or ring measure blood pressure accurately while you sleep?

KnowYourPrime evidence ratingUncertainEvidence is conflicting, inconsistent, or difficult to interpret.

Not yet. Across pooled studies, cuffless devices agreed with 24-hour cuff monitoring during the day but read significantly higher at night, and an Aktiia bracelet worn by 41 people read nighttime systolic pressure 15.5 mmHg higher than the cuff monitor, understating the normal overnight dip.

Finding KYP-ER-0021Version 1.0Reviewed October 24, 2026Rating rule 1.6CC BY 4.0

Why this is rated Uncertain

Nighttime blood pressure carries strong prognostic weight, and the overnight dip is one of the things a 24-hour cuff monitor exists to measure. A meta-analysis of cuffless devices against 24-hour monitoring found daytime agreement and significant nighttime differences, and concluded current devices are not reliable at night.

One watch-like sensor study reported small nighttime differences and is the clean anchor, but two studies of the Aktiia bracelet found nighttime readings markedly higher than the cuff. The rule rates the claim Uncertain.

How the rating rule reads this evidence

Anchor-grade evidence affirms the core relationship.
Multiple supporting studies are consistent with the core relationship.
An anchor study is present but its own reported finding does not cleanly affirm this claim, so it does not count toward the Established threshold.
The claim rests on a single anchor whose finding affirms it; a second independent affirming anchor is needed to reach Established.
A clean anchor supports this claim, but an unresolved conflicting study contradicts it on the core relationship, so the evidence is treated as in genuine dispute.

Key results

In a meta-analysis of studies from 2019 to 2024, cuffless devices differed from 24-hour ambulatory monitoring by -0.99 mmHg systolic in the daytime (95 percent CI -3.47 to 1.49) but by 4.48 mmHg systolic (0.27 to 8.69) and 5.64 mmHg diastolic (2.57 to 8.71) at night. (Lee et al., American Journal of Preventive Cardiology, 2025)
In 41 participants wearing the Aktiia bracelet for 6 to 12 days, nighttime systolic pressure averaged 15.5 mmHg higher than ambulatory monitoring (95 percent CI 11.8 to 19.1) and diastolic 11.8 mmHg higher, while daytime systolic was similar (1.0 mmHg). (Tan et al., Journal of Hypertension, 2023)
A watch-like optical sensor worn during conventional 24-hour monitoring showed small average nighttime differences, and its authors concluded cuffless 24-hour monitoring may become a clinical possibility. (Proença et al., Scientific Reports, 2023)

What this finding covers

Applies to: Cuffless wearables that estimate blood pressure from optical or other signals, compared with 24-hour ambulatory cuff monitoring, especially at night.

Does not cover: Watches with a built-in cuff, covered separately; hypertension notifications that report no number; diagnosis.

Limitations

Devices use different technologies, so pooled results may not apply to any one product.
Several studies are small, and some authors have ties to device makers.

Evidence base

7 studies scored · 2 anchor · 2 conflicting · 3 supporting · Evidence last evaluated Oct 19, 2026

Anchor studies

The studies the rating rests on.

Comparing the accuracy of continuous blood pressure monitoring using wearable cuffless devices with conventional 24-hour ambulatory blood pressure monitoring: A systematic review and meta-analysisLee et al., American Journal of Preventive Cardiology, 2025. doi.org/10.1016/j.ajpc.2025.101342
Method-comparison study between a watch-like sensor and a cuff-based device for 24-h ambulatory blood pressure monitoring.Proença et al., Scientific Reports, 2023. doi.org/10.1038/s41598-023-33205-z [conflict statement: the authors' institute holds the patent on the method tested, and two authors are its inventors]

Conflicting studies

Studies whose findings run against the claim.

Evaluation of Aktiia cuffless blood pressure monitor across 24-h, daytime, and night-time measurements versus ambulatory monitoring: a prospective, single-centre observational study.Almeida et al., Journal of Hypertension, 2025. doi.org/10.1097/HJH.0000000000003960 [author affiliations include Aktiia]
Evaluation of the ability of a commercially available cuffless wearable device to track blood pressure changesTan et al., Journal of Hypertension, 2023. doi.org/10.1097/hjh.0000000000003428 [conflict statement: Aktiia supplied the devices tested, and two authors have been paid by Aktiia]

Supporting studies

Studies consistent with the claim that do not carry the rating on their own.

Photoplethysmography based remote cardiac blood pressure monitoring compared with 24-h ambulatory blood pressure monitoring.Vliet et al., Blood Pressure Monitoring, 2026. doi.org/10.1097/MBP.0000000000000804
Validation of ring-type cuffless blood pressure (BP) monitoring device for detecting awake-asleep BP variations compared to ambulatory BP monitoring device.Lee et al., Hypertension Research, 2026. doi.org/10.1038/s41440-026-02759-6 [funding statement: sponsored by Sky Labs, maker of the CART BP ring tested, which took part in study design and data collection]
Nocturnal Blood Pressure Estimation from Sleep Plethysmography Using Machine Learning.Yilmaz et al., Sensors, 2024. doi.org/10.3390/s23187931

Version history

Version	Date	Rating	Change
1.0	October 24, 2026	Uncertain	First published.

Rating history on the research desk: Uncertain (October 19, 2026).

Cite this finding

KnowYourPrime Evidence Registry, Finding KYP-ER-0021, version 1.0, reviewed 2026-10-24. https://knowyourprime.com/evidence-cuffless-blood-pressure-at-night

Machine-readable: JSON · Markdown · All findings

Research desk: the blood pressure research desk entry for this question, with every scored study and its role
Related finding: Do Calibrated Cuffless Blood Pressure Readings Track Real Changes? (KYP-ER-0022)
Related finding: Accuracy of Smartwatches With a Built-In Blood Pressure Cuff (KYP-ER-0020)
On this site: Can a Smartwatch or Ring Really Measure Blood Pressure?
On this site: Does a Cuffless Blood Pressure Wearable Actually Work?

This is KnowYourPrime's own assessment of the published evidence, rated under the KnowYourPrime evidence methodology. The rating is set by a fixed rule from the roles of the studies above and moves only when the evidence or the rule changes. Every change to the rating or the text is published as a new dated version. To report an error, write to corrections@knowyourprime.com.