Strong emotions lead to an increase of the pulse rate, thus this biometric measure is certainly the best known from everyday life and requires little further explanation. It can be measured very simple optically via a sensor on the finger or if an ECG is measured, it can also be derived directly from this. The today common pulse watches and fitness tracker also provide a pulse rate. However, this is very inaccurate because beats are sometimes skipped by theses devices, which is sufficient for tracking of fitness but leads to artifacts in experiments and may cause misinterpretation.
Significance for the emotional intensity: high
Informative value on the kind of emotion: low
Informative value on the mental workload: low
Effort: extractable via a pulse oximeter (finger clip) or from an ECG