Monitoring the electromechanical activity of the heart in non-hospital settings is now a reality. This is achieved by estimating the time between the Q wave of the electrocardiogram (ECG) and the peak of the S2 sound of the phonocardiogram (PCG) (QS2 interval). Currently, various chest-worn devices assess cardiovascular health, but they rely on detecting the ECG and photoplethysmogram (PPG). In this work, we proposed a novel chest-worn device that simultaneously detects the ECG and the PCG, which could be a valuable tool for estimating the QS2 interval. The device consisted of two dry electrodes to detect the ECG and a PVDF piezoelectric sensor to detect the PCG, all coupled in a custom-made chest strap. The device was tested on 15 healthy subjects at rest, during physical activity, and during recovery, to evaluate its performance across different physiological states. The device consumed 150 µA, allowing for over 69 days of continuous use with a 3.7 V/250 mAh battery. The system demonstrated its ability to detect the principal ECG waves (PQRST) and the principal PCG sounds (S1 and S2) both at rest and after physical activity, allowing the QS2 interval to be estimated at different heart rate values, provided the subject remains still during the measurement. When 60 Hz interference was high, the ECG Q and S waves could not be detected. The proposed system offers an alternative for continuous cardiac monitoring in non-ambulatory settings, with significant potential for integration into AI-based platforms for early diagnosis and personalized patient care.