Many homes have them, but many homeowners don't know how their alarm systems work.

You need to know though because on Monday, the analog system will not work -- which could affect security systems, which contact authorities via cellular networks when triggered.

Most newer systems installed are digital, but if upgrades are needed it could cost you. Richard Dietz of Dietz Electronics said security system customers could pay between $200 and $800 for new systems. Security experts said providers should be able to make the switch from analog to digital for existing customers at no charge. Customers should check with their provider for the potential cost and deadline.

Some car owners will have bigger troubles when analog doesn't exist. If your car is older than a 2004 or 2005 model, there is no OnStar upgrade available.

Analog cell phone service will also cease as carriers drop the aging networks. The changes will not affect a majority of cell phone users, however, because most customers have phones that communicate on the digital networks.