See simple Infrared Intruder Alarm circuit. Even it is best. But it is a good teacher to learn electronics. Using infra-red system.
Here is five burglar alarm circuits for you can look as idea To protect their property from thieves. simple switching, vibration systems, touch-sensitive.
You have a private area, right? If you have this motion detector alarm circuit. It will reduce your worries. Imagine a big bear is coming to the behind of your house. Then, the siren alert. The big bear is shocked and runs away. You and your family are safe. Is it great?