Crowtail- Bluetooth Low Energy Module HM-13 is an easy to use module compatible with the existing Crowtail Base Shield, and designed for transparent wireless serial connection setup. The serial port Bluetooth module is fully qualified BT Version V4.0 EDR + BLE dual mode with complete 2.4GHz radio transceiver and baseband. It has the smallest footprint of 13.8mm x 18mm. Hope it will simplify your overall design/development cycle.