This will layout basic operation, newer features are being added and this won't reflect that.
This project uses two linked up NRF modules attached to Arduino Uno's (communicates via SPI protocol). The "transmitter" (I'm leaving bidirection comms in for now, as opposed to one-way, for increased reliability; if this starts getting attacked it won't make much difference making it one-way comms with no acknowledgements and no CRC) is constantly listening on an assigned pin to go low to begin transmitting an activation of the sensor to the receiver.
Once that digital pin goes low, this commences to encrypt a microsecond timer and a bit of entropy with the XTEA cipher. This is to confuse any eavesdropper what's passing through wireless channels if they happened to have found the channel.
The receiver decrypts this packet, it doesn't matter what the packet contains (right now, that will likely change due to authentication concerns), main thing is the channel chosen and the address of the receiver/transmitter that is most of the authentication happening right now which is insufficient.
After receiver confirms with transmitter, a user chosen byte value is written to internal EEPROM. If user wants to check how many activations happen, you have to count hex bytes in the EEPROM. There are read EEPROM programs you can load up and read via Arduino Serial Monitor, amongst other ways to read out this data.
This is the gist of the operation of this project. More features to hopefully make it harder to hack, if I can implement them, will be added.