Azumio’s Instant Heart Rate app lets you do quick heart rate measurements using nothing more than the camera in your mobile device. This works well when you are holding still, so it’s a great way to get resting heart rate measurements, e.g. every morning before you get up.
If you wanted to use your heart rate measurements with other data you have in Zenobase (e.g. to see how your resting heart rate correlates with sleep or exercise), and you are on Android, you can connect the Instant Heart Rate app to Google Fit, and import the data into Zenobase using the google-cardio task.
Caveats: Azumio reports the measurement as a time range, with a begin that is one hour prior to the actual measurement. Also, the app sometimes forgets to send data to Google Fit, and needs to be reconnected.