A better Dummy Alarm .. uses the MK111 timer

I bought and built MK126 which is the Dummy Alarm kit. But I was not impressed with the flash frequency which was intermittent and unrealistic. Sometimes it would come on if I cranked up the volume on my stereo.

So I came up with a better solution: Modify MK111 which is the simple 555 timer kit. This kit is set up such that the timer controls the relay. By cutting two tracings and adding three jumper wires, I rewired it such that the relay controls the timer circuit.

Now I have a continuous 12v wire that goes to the NC relay contacts which activates the timer flash. When I turn on the ignition, the relay is on which turns off the timer. Easy mod … and a nice panel mounted LED (3v) is available from Radio Shack for $3.

ok what you do is:

Cut the foil between 12v and the diode D3
Cut the foil between the NO (normally open) output and the NO solder point on the relay.
Make a jumper wire from 12v to NC (normally closed)
Make a jumper wire from COM to diode D3
Make a jumper wire from NO to relay positive point on the relay (near the edge of the circuit board)

Constant 12v is connected to 12v terminal (stereo preset memory?)
Switched 12v is connected to Normally Open terminal (stereo power on?)
Ground is connected to Ground.

What happens is … when the car is off, power is routed through the NC (normally closed) contact via the COM connection to diode D3 to operate the timer circuit to make the diode flash.
When the car is on, switched power energizes the relay which switches the contacts to NO (normally on), thus switching off the power to the timer circuit.

Adjust the two pots to get the rate and duration of LED flash. Find a nice dash mounted LED at radio shack for $3. This makes for a much more realistic dummy alarm than the MK125 kit which flashes erratically.

Rob (Atlanta, Georgia)

Recently a friend said that my car does have a car alarm!

Hi Rob, you still around ?? Eddie in the UK here.
I seem to have the same problem as you with the MK126 and timings etc., I have posted a request to support but don’t know whether the MK126 will give me the short flash every 2 seconds that I am looking for.
I am interested in your solution but, being new to electronics, I am a little confused by the terminology.
By “cut the foil” do you mean cut the actual tracking on the MK111 PCB ??
Regarding jumpers etc., would it be possible for you to provide a diagram of where the jumpers and going from/to, it would be much appreciated.
I can let you have my e-mail if it would make things easier.
Regards, Eddie

Yes … I use a small jewlers screwdriver to “grind” across the foil tracing … which exposes the white board underneath. This is easy to do and typically you do not need to use a multimeter to double check your efforts.

The jumpers are insulated wire cut to length to make connections between two solder points.

The MK111 circuit is designed to activate the relay… By making the five changes, the relay deactivates the circuit. (My mod is still working well in my car for several years now and my nephew built and installed this in his car also.)

I suggest that you download the MK111 circuit diagram and mark the changes to understand what is going on.

You will use your LED from the MK126 as before and mount the circuit in a small plastic box to prevent shorts.

Thanks Rob, I will give it a go in the New Year.