The Intel Hex File has emerged in recent decades as a standard for firmware transfer in microcontrollers. The weakness of this format is reflected in the uncertainty of the checksum. This work has set itself the task to develop a transmission method which allows a better error detection. In the first part the problem of the Intel Hex File is considered. There are various ways in which the transfer of data can be resolved more securely. A solution is then implemented using an Atmegas238 and a Bluetooth module. In this case, both the bootloader code and a suitable Windows client are implemented to verify and confirm the transmission security function.