RF transmittor to GSM module_How do you do it???

[STORBOY12]

Design application problem..RF transmittors to GSM module

I'm trying to figure out how to connect 20-30 medium range (500m) RF transmittors to a micro-controller or RF reciever which is then connected to a GSM module.

My plan is to monitor 20-30 outdoor doors/ exits closing only, so have the idea of setting up a reed switch (which sends signal when door closes) which is hardwired to an RF transmittor which sends a signal to the RF receiver which is hardwired to a GSM module.

The output wanted is an SMS stating something like "gate 4 closed"

I'm a total electronics novice,so any info /help would be great.
If I bought 20-30 RF transmittors ,how would they be identified in the application??

 

[FvM]

how would they be identified in the application?

Obviously, they need to transmit an unique code. A Holtek HT12 remore control encoder e.g. could do. You should also
think about when you want to send exactly. Sending permanently on contact closure would block other transmitters and
exhaust the battery quickly (and also not comply with small radio regulations), sending only once can be missed. Sending once
on closure and a repeated status update from time to time would be more reliable.

At the receiver, you surely need a small computer respectively microprocessor to convert the received information to SMS.
It's not particularly an electronics rather than programming or data processing problem.