Remote Keyless Entry (RKE) systems are essential in modern lifestyle with applications including vehicle and garage entry. However, the convenience such systems facilitate comes at the expense of their vulnerability to different attacks such as jamming, replay, jamming-and-replay, and cryptanalysis. These attacks, if lightly taken, may lead to catastrophic consequences to the general public, such as property theft and human casualties. To this end, an improved RKE system using timestamping and XOR encoding is proposed to countermeasure the aforementioned attacks. In addition, the integrated defense mechanism protects the authentication code in scenarios where the encrypted transmitter-receiver communications are compromised. The defense mechanism in the proposed RKE is demonstrated and tested in realistic setups, and is found to outperform the conventional RKE.