Smart watches in future will have smart wristband. This work analyses properties of new developed capacitive wristband sensor that measures ballistocardiogram (BCG) from single point on the wrist. In addition, it considers applications of this sensor to monitoring heart rate variability. Another application is in estimating changes (trend) in systolic blood pressure continuously when combined with lead one electrocardiogram (ECG). BP is one of the vital signs that indicates the health condition. It is commonly measured by cuff-based monitor using either auscultatory or oscillometric method. Cuff-based BP monitor is not portable and unable to measure BP continuously which means it is difficult to attach BP monitoring function on a wearable device. Significant research is conducted in estimating BP from pulse transit time (PTT) mathematically which would enable the cuffless BP measurement. In this work, a new time reference, RJ interval, which is the time delay between ECG and BCG signal peaks was tested whether it can be used as a surrogate of PTT in cuffless BP estimation. Based on the study done on 10 healthy people, it was shown that RJ intervals can be useful in evaluating trends of systolic blood pressure.