Firmware hex files
To upload a new hex file to the SensorTag you need a CC Debugger and TI's SmartRF Flash Programmer.
Connect the 10 pin flat cable (1.27 mm pitch) which is included with the CC Debugger, to the debug header (J1) on the SensorTag as shown here.
Over the Air Download
For the latest release of the SensorTag Firmware can be uploaded through the SensorTag app or by using the BLE Device Monitor using Over-the-Air-Download (OAD). OAD is supported in the TI BLE stack version 1.3 and newer. Read more about OAD in the User Guide
Download here: SensorTag Firmware rev 1.5
Revision 1.5 of the SensorTag firmware is the same version as in TI's Bluetooth low energy SW stack 1.4.0, . The package Includes a hex image which can be used with a CC debugger and bin files for over the air download.
Download here: SensorTag Firmware rev 1.4
FW with 8G accelerometer resolution and 1 second barometer period
Download here: SensorTag 8G
Source code for MAC OS X application example
Download here: SensorTag OS X example
Source code of SensorTag and other BLE projects is included in http://www.ti.com/tool/ble-stack