Query regarding working of telephone

[reubenn]

hello everybody, i'm currently working on my final year project
this is the idea it is based on:
a circuit (transmitter) mounted on a door is made to send a pulsed IR beam across to a circuit (receiver) mounted on the wall adjacent to the door.
a microcontroller monitoring the receiver circuit knows when the beam is interrupted, if the door is opened,and is used to place a call using a landline telephone.

When somebody picks up a landline telephone and dials a number, he knows when the called party has picked up the telephone.
Im using a microcontroller in the above circuit. Lets say the system is switched ON and an intruder breaks into the house. Using the process called "pulse dialling"(a system of dialling used by the earlier phones still available on modern phones, see here to understand properly :
https://en.wikipedia.org/wiki/Pulse_dialing), the microcontroller can dial a pre-determined number.
Trouble is , how does the microcontroller recognize that the called party has picked up the phone and play the voice message?
What are the signals involved when a call is placed and connected ?

Can somebody please tell me how a call is placed using a landline phone, and what signal is sent back to the calling party when the called party has picked up the phone?

Is there any site which will guide me wrt my query

 

[FvM]

There is no off-hook signal send on analog phone lines. So all automatic speech dialers (they are used since decades) have basically the problem of detecting that the intended receiver is listening. One option is to delay the message during calling tone, another to repeat the message e.g. 4 times. If an acknowledgment (by a dial tone) is required, message failure can be assumed then.