Ecg electrodes for wearable physiological monitors

A wearable monitor comprising:

• a housing with an exterior surface and an interior space;
• electrocardiogram circuitry in the interior space of the housing;
• a first electrode, wherein:
• the first electrode is positioned for access by a user when the wearable monitor is placed for use on the user, and
• the first electrode is removably and replaceably coupled to the housing;
• and
• a second electrode, wherein:
• the second electrode is positioned on the exterior surface of the housing,
• the second electrode is positioned to contact a skin of the user when the wearable monitor is placed for use on the user, and
• the second electrode is coupled to the first electrode through the electrocardiogram circuitry in the housing.

A computer program product comprising computer executable code embodied in a non-transitory computer readable medium that, when executing on one or more processors of a wearable monitor, causes the wearable monitor to perform the steps of:

• monitoring two or more electrodes of a wearable monitor, wherein:
• the two or more electrodes including a first electrode and a second electrode,
• the second electrode is in continuous contact with a skin of a user of the wearable monitor when the wearable monitor is placed for use on the user, and
• the wearable monitor is configured to acquire electrocardiographic data with the two or more electrodes;
• receiving a hardware interrupt with the wearable monitor, the hardware interrupt responsive to a predetermined impedance between the first electrode and the second electrode, and the predetermined impedance indicative of user contact with the first electrode;
• while the hardware interrupt indicates the predetermined impedance between the first electrode and the second electrode, periodically incrementing a counter;
• and
• in response to the counter meeting a second predetermined threshold, generating a button press signal to a process executing on the wearable monitor.