44 Chapter 5. THE LADDIE ALARM SYSTEM: A SAMPLE APPLIANCE Previous chapters covered how to build and secure a daemon and how to communicate with the daemon while it is running. We'll tie these topics together in this chapter by building Laddie , a Linux- based alarm system. 1 Laddie uses the five status inputs on a standard PC parallel port as sensor inputs to the alarm system. The heart of the Laddie appliance is the ladd (pronounced lad-dee ) daemon that polls the status lines and reports input transitions using syslog(). An alarm system is a good choice for a sample application since most readers will have some familiarity with alarm systems and because an alarm system application is simple to write, understand, and modify. This chapter includes the following five sections: · Introduction to alarm systems