A system for operating a wearable device (203, 403) dependent on whether or not the wearable device is worn, comprising: a wearable device (203, 403) configured to operate in at least a connected and a disconnected state and including a photoplethysmographic sensor configured to detect a body part of a user; an attachment member (202A, 202B, 402) configured to attach the wearable device (203, 403) to the body part of the user, wherein the attachment member (202A, 202B, 402) is configured to transition between a disconnected configuration and a connected configuration, and wherein the attachment member (202A, 202B, 402) is configured to attach the wearable device (203, 403) to the body part of the user in the connected configuration; characterized in that: the wearable device (203, 403) is configured to switch from the disconnected state to the connected state upon: the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the disconnected configuration to the connected configuration, the photoplethysmographic sensor attempting to detect the body part of the user after the wearable device detects that the attachment member transitions from the disconnected configuration to the connected configuration, and the photoplethysmographic sensor detecting the body part of the user; and wherein the wearable device (203, 403) is configured to switch from the connected state to the disconnected state upon: the photoplethysmographic sensor periodically attempting to detect the body part of a user and the photoplethysmographic sensor not detecting the body part of the user; and the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the connected configuration to the disconnected configuration. a wearable device (203, 403) configured to operate in at least a connected and a disconnected state and including a photoplethysmographic sensor configured to detect a body part of a user; an attachment member (202A, 202B, 402) configured to attach the wearable device (203, 403) to the body part of the user, wherein the attachment member (202A, 202B, 402) is configured to transition between a disconnected configuration and a connected configuration, and wherein the attachment member (202A, 202B, 402) is configured to attach the wearable device (203, 403) to the body part of the user in the connected configuration; characterized in that: the wearable device (203, 403) is configured to switch from the disconnected state to the connected state upon: the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the disconnected configuration to the connected configuration, the photoplethysmographic sensor attempting to detect the body part of the user after the wearable device detects that the attachment member transitions from the disconnected configuration to the connected configuration, and the photoplethysmographic sensor detecting the body part of the user; and wherein the wearable device (203, 403) is configured to switch from the connected state to the disconnected state upon: the photoplethysmographic sensor periodically attempting to detect the body part of a user and the photoplethysmographic sensor not detecting the body part of the user; and the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the connected configuration to the disconnected configuration. the wearable device (203, 403) is configured to switch from the disconnected state to the connected state upon: the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the disconnected configuration to the connected configuration, the photoplethysmographic sensor attempting to detect the body part of the user after the wearable device detects that the attachment member transitions from the disconnected configuration to the connected configuration, and the photoplethysmographic sensor detecting the body part of the user; and wherein the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the disconnected configuration to the connected configuration, the photoplethysmographic sensor attempting to detect the body part of the user after the wearable device detects that the attachment member transitions from the disconnected configuration to the connected configuration, and the photoplethysmographic sensor detecting the body part of the user; and wherein the wearable device (203, 403) is configured to switch from the connected state to the disconnected state upon: the photoplethysmographic sensor periodically attempting to detect the body part of a user and the photoplethysmographic sensor not detecting the body part of the user; and the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the connected configuration to the disconnected configuration. the photoplethysmographic sensor periodically attempting to detect the body part of a user and the photoplethysmographic sensor not detecting the body part of the user; and the wearable device (203, 403) detecting that the attachment member (202A, 202B, 402) transitions from the connected configuration to the disconnected configuration.