It could be beeping for a variety of reasons - anything from a low battery to the system trying to inform you of a communication failure, or a previous event. Depends on a number of things. Also, not sure what you mean by "inactive" - does that mean non-monitored, and completely not in use? Sorry for the questions, but there are many variables, and while SIA (the Security Industry Association) and UL have reached agreement on a number of protocols, there are just too many equipment makers out there (to say nothing of the age and model of yours) to hazard a guess on what is happening with your system. Any details you can provide would help!
By the way, I would think twice about leaving the system inactive...In the first place, the FBI reported that in 2008 a burglary occurred in the US every 15 seconds, with an average loss of over $2,000. Have not seen the 2009 stats yet, but they are expected to be even scarier. Now for the clincher: home without a monitored alarm system are three times more likely to be burglarized than homes with a system. That is a huge advantage for the alarm owner - and while having a system may not prevent a break-in, it can clearly deter one.
By the way, when it comes to alarm systems, the only safe ones use cellular monitoring (no phone line required, no phone line to cut!). Anything else is old news, since even an internet connection is easy to cut. Plus, the alarm company should not charge extra for the cell radio, or add on big monthly fees for cell monitoring. The next thing to look for is interactive services: remote arm/disarm, special apps for hand-held devices, text and email notifications, and even video and smart home features. In other words, the game has changed, and the traditional "big boys" are way behind. And you can get a great system that you can install yourself, fully programmed and ready out of the box. That means you can add devices at any time, and even move the system with you. When researching, I strongly recommend that you look at all the reviews you can find, and Google is a good place to start. Shop hard, and don't just focus on the big names: there are providers covering the Canada and the US that are doing a much better job, and you can check them out very easily. Look for safer, smarter, simpler, and more affordable - you will be happy you did!
With over 20 years in the alarm industry, I work for FrontPoint Security (www.frontpointsecurity.com), a leading nationwide wireless home security provider. Our company offers cellular monitoring and next generation features the “big boy” traditional companies have not figured out yet. I am offering this advice to increase awareness of what alarm systems can (and should!) do. The more we all know, the better!