This post gives you the hardware overview of BioAmp EXG Pill v0.7 and shows how it can be interfaced to Arduino Uno and run the examples to read ECG and heart beat.
Tutorial on interfacing R307 optical fingerprint scanner with Arduino development boards along with Arduino library. Fingerprint scanners can be used for biometric authentication.
Tutorial on interfacing Silicon Labs CP2102 USB-Serial chip with any microcontroller. Instructions to install driver, block diagram, pinout, and pin descriptions included.
Tutorial on interfacing Intersil/Renesas ISL1208 Real-Time Clock chip with Arduino boards through I2C interface. Arduino compatible library and example code are included.