Listen to your intuition as to whether your system is being installed by a trustworthy home security company. This is particularly true if you're uneasy with those that install your actual system. There is nothing wrong with asking for a different technician if you're uneasy. Your security system is supposed to help you, not cause you more stress.
Don't just hide your spare key anywhere. It is very common for homeowners to hide them under a mat or above the framing of their door, and intruders know this. Rather, think about putting a key on your outside dog's collar.
Dogs are among the most effective home burglary systems. Dogs naturally protect their homes and they make lots o