Electronics 2000

I would be really grateful if somebody could help us with how to go about making or modify an existing alarm type device or a least getting to grips with a circuit diagram that I can work from, for this problem?

Last week our dog escaped ( please don't laugh) and was missing for three days in total. It was a total disaster for the family but least we got him back.

He escaped because my wife opened the door to let him out of the kitchen, not realising that the garden gate was open further up the passageway. On our particular house viewing the garden gate is closed is not straightforward so what I'm looking for is a simple device/alarm that if either our kitchen door or our gate is opened separately will not sound, but if both are open together - will sound an alarm.
Sounds pretty straightforward but I cannot get round the idea of two open circuits producing this result.
Gosh I'll be extremely grateful if anybody could point me in the right direction Best regards Steve H

You need two switches which will be on (i.e. contacts closed) when the doors are open. Wire them in series with a power supply and bell/sounder/light/etc.

Hope this helps

Put a spring on the garden gate?

You need an AND gate TTL IC two switches and an LED or buzzer and a battery or power supply.

Tar&stuff.

Put a garden shed alarm on the door you need protected.If you buy the type that has a wire running from the control box to the sensor switch, then you can extend the wire,and install the control unit inside, somewhere convenient for use.