"Secure type 433 Mhz RF transmitter" means that each transmiter has unique 16 bit ID which can be set to unique and no two transmitter ID has same IDs. When ever the transmitter is transmitting data it sends its ID first then the data part. The data part can contain bits of information like which key is pressed.
To implement a secure remote application where only particular transmitter has to be acted upon by the receiver it is required by receiver/decoder to store the transmitter ID before it stars working.
The receiver/decoder has to store the ID of the transmitter in its internal memory and compare each IDs with received packet before acting on the data from transmitter. Due to this approach very secure, reliable remote control applications can be made.
Lets consider an example of what secure means here. In an application we want to implement a remote control for Main Gate opening. In this case each person has one remote transmitter with them. When a person who is allowed access press a switch, the decoder first looks in its internal memory if that ID is already pre-stored then only it acts on the data else ignores it. That means if there are 10 transmitters working, each IDs has to be pre-stored in the IC for it to allow access.
Also if there are many transmitters working in same range, its still secure protocol. They should not interfere or false transmit or trigger false manner. These all problems have been considered while designing this secure type 433 Mhz RF transmitter.
Block Diagram of working