A major conventional car key is the mechanical key. When users inserted the key into a cylinder mechanical key and turn, users can unlock. The mechanical key may be able to be worn away for physical contact. And it may be impossible to use. Further the mechanical key may be damaged or destroyed by mischief. So a keyless entry system has been developed. The keyless entry system locks and unlocks using the infrared ray and radio waves communication. The keyless entry system does not require physical contacts. Therefore, the possibilities of damage due to mischief and be worn away are fell. However, the transmission ranges of infrared ray and radio waves communication are not clear. Submitting data might be tapped to the malicious people. If the information is tapped, then you have theft of the car and the risk of car break.