hi guys this is my first instructable i hope you'll enjoy it !!

Got sick of the high prices of Home Security systems ??
have old mobile sets don't know what to do with ?
build a cheap alarm system that will notify you on your mobile by SMS.
ready ??

grab the tools !

Step 1: What You'll Need

An old mobile phone set with supply (charger).
Cheap door magnetic alarm (can be replaced by a magnetic switch and a magnet ).
5 volts Relay.
Soldering iron.
wires and thin insulated copper wires.
micro driller.
micro screwdriver set.
clipper.
multimeter.
Scotch tape.

Step 2: Let's Get to Work

here is the whole thing....you write the text message " for example : the main door was opened " then you put your mobile number then you...don't press the sending button.... you'll make the burglar do it !
you just want the magnetic switch to work as the sending button.

but unfortunately most of the alarms on the market contains an NO "normally-open" magnetic switch
so when the magnetic field applies "that means the door is closed ", the switch closes. and that means also that when the door is opened the magnetic field vanishes and the switch is opened..
we need the opposite of that we need the switch is closed when the door is opened and vise versa

what will we do ?? you can just seek a SPDT "Single Pole Double Throw" magnetic switch from components shops this should solve the problem of the whole alarm, but this was hard to find so i used a relay powered by the mobile charger to do the job..

The other problem is that some mobile sets closes the keypad automatically or switch to standby mode after a period of time "in order to save energy" but most of old ones doesn't... you just have to go to settings and turn of the automatic keypad lock.

if your mobile does closes the keypad automatically or switches to stand buy mode then you'll have to build a small 555 timer circuit that will trigger any unvital key on the keypad like the volume control " every 3 sec for example " to keep it on the send message mode.. of course the mobile should be powered from the charger all the time.

Step 3: Preparing the Mobile Set...

Most of Nokia old mobiles are easy to deal with they don't standby and you can disable the auto keypad lock .
I used nokia 6210 and soldered two wires to the OK button "Upper left":

Step 4: Preparing the Magnetic Alarm...

In this step you'll just solder two wires to the two terminals of the magnetic switch inside.
and drill two holes for the two wires
the batteries in the alarm aren't necessary at all unless you want to keep the noisy alarm

NOTE : you have to test your alarm first, you may not need a relay at all test the magnetic switch with the multimeter to know whether it is NC or NO.

Step 5: Prepairing the Relay and Final Connection

The relay is simply a switch which is turned on or of by an electrical magnet when you apply current on the coil it operates the relay
but the problem is that the relay coil needs power to work , a good idea is to take the DC of the charger
"as the mobile will be always be connected to the charger "

Step 6: Test It Now ....

After checking the wiring and preparing the text your alarm system should be ready
just mount the the magnet on the door and the set on the frame , plug the charger into mains , switch on the mobile open the message and put the mobile number...

of course it's better to mount it in casing or something ...

now it's ready !

waiting for your comments and suggestions : )