# SRPhotoplethysmogramSample The sample photoplethysmogram (PPG) sensor data. ``` class SRPhotoplethysmogramSample ``` ## Overview The PPG sensor provides an array of these objects as its [`sample`](/documentation/SensorKit/SRFetchResult/sample) type. Apple Watch uses LED lights, paired with light-sensitive photodiodes (PD), to track the heartbeat-induced pulsations. Different Apple Watch models can have different numbers of LEDs and PDs. For more information, see [`SRPhotoplethysmogramOpticalSample`](/documentation/SensorKit/SRPhotoplethysmogramOpticalSample). For more details, see: - [Monitor your heart rate with Apple Watch](https://support.apple.com/en-us/HT204666) - [Using Apple Watch for Arrhythmia Detection](https://www.apple.com/healthcare/docs/site/Apple_Watch_Arrhythmia_Detection.pdf) - [How to use the Blood Oxygen app on Apple Watch](https://support.apple.com/en-us/HT211027) - [Blood Oxygen app on Apple Watch](https://www.apple.com/healthcare/docs/site/Blood_Oxygen_app_on_Apple_Watch_October_2022.pdf) ## Topics ### Accessing PPG data [`var startDate: Date`](/documentation/SensorKit/SRPhotoplethysmogramSample/startDate) The start date of the photoplethysmogram (PPG) sensor data recording. [`var nanosecondsSinceStart: Int64`](/documentation/SensorKit/SRPhotoplethysmogramSample/nanosecondsSinceStart) The time in nanoseconds since the start of the data recording. [`var usage: [SRPhotoplethysmogramSample.Usage]`](/documentation/SensorKit/SRPhotoplethysmogramSample/usage-swift.property) The method that the person or system uses to take the reading. [`struct Usage`](/documentation/SensorKit/SRPhotoplethysmogramSample/Usage-swift.struct) The possible ways that a person or the system may take a photoplethysmogram (PPG) reading. [`var opticalSamples: [SRPhotoplethysmogramOpticalSample]`](/documentation/SensorKit/SRPhotoplethysmogramSample/opticalSamples) The samples recorded by the photoplethysmogram (PPG) optical sensor. [`class SRPhotoplethysmogramOpticalSample`](/documentation/SensorKit/SRPhotoplethysmogramOpticalSample) A data sample from the photoplethysmogram (PPG) optical sensor. [`var accelerometerSamples: [SRPhotoplethysmogramAccelerometerSample]`](/documentation/SensorKit/SRPhotoplethysmogramSample/accelerometerSamples) The samples recorded by the photoplethysmogram (PPG) accelerometer. [`class SRPhotoplethysmogramAccelerometerSample`](/documentation/SensorKit/SRPhotoplethysmogramAccelerometerSample) A data sample from the photoplethysmogram (PPG) accelerometer. [`var temperature: Measurement?`](/documentation/SensorKit/SRPhotoplethysmogramSample/temperature) The samples recorded by the photoplethysmogram (PPG) thermometer. ## Relationships ### Conforms To [`CustomStringConvertible`](/documentation/Swift/CustomStringConvertible) [`CVarArg`](/documentation/Swift/CVarArg) [`NSCopying`](/documentation/Foundation/NSCopying) [`Sendable`](/documentation/Swift/Sendable) [`CustomDebugStringConvertible`](/documentation/Swift/CustomDebugStringConvertible) [`NSSecureCoding`](/documentation/Foundation/NSSecureCoding) [`NSCoding`](/documentation/Foundation/NSCoding) [`Hashable`](/documentation/Swift/Hashable) [`Equatable`](/documentation/Swift/Equatable) [`SendableMetatype`](/documentation/Swift/SendableMetatype) [`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol) ### Inherits From [`NSObject-swift.class`](/documentation/ObjectiveC/NSObject-swift.class) --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)