Cardiovascular diseases (CVDs) pose a significant global health challenge that requires innovative solutions for continuous monitoring and early intervention. Different solutions are part of healthcare digital transformation through mobile implementations. In this paper, presented a lead electrode-based and cross-platform-supported ECG device called CorSeg, which is suitable for monitoring heart activities in home and outdoor environments. Additional functionalities are body temperature measurement and movement detection for removing motion artifacts and calculating heartbeat rate. An ESP32-PICO-D4 integrated microcontroller board called ESP32 PICO KIT D4 has been used to obtain and process the ECG data. A cross-platform supported software has been developed with a .NET MAUI framework to store and visualise the ECG data. To send and receive data between the CorSeg device and the cross-platform software, Universal Serial Bus (USB) and Bluetooth communication protocols have been used. The activation of the protocols depends on the device where the software is installed. For mobile devices, the CorSeg ECG device uses Bluetooth communication, while it uses USB for desktop devices. The CorSeg device has been tested with the FLUKE ECG simulator in a laboratory environment, where the simulation and real-life test on volunteers suggest that the device's performance is good enough to monitor heart rhythm. The device is fabricated with a 3D-printed box so that the user can put the box in their pocket during walking.