The cost of home security and surveillance systems has decreased so that now everybody can afford a system. Internet providers offer home security systems. Some people use hidden cameras like nanny cams to keep an eye on babysitters. The news contains stories of people who use home security systems to catch burglers in the act. While such security systesm have many benefits they can also cause people to commit criminal acts.
Most states have laws that prohibit recording of voice communications without permission or a court order. These are generally called wiretapping laws. While we usually think of wiretapping as meaning telephone calls the laws are usually written broadly to cover all voice communications. Some states allow recording of such conversations if one person to the conversation gives permission. Other states, including Massachusetts, require all parties to the conversation to grant permission before the conversation can be recorded. Recording a conversation without permission is a crime in most states. In Massachusetts, making an unathorized voice recording is a felony. This means that making a recording of a person's voice without their permission can result in person being sentenced to imprisonment in the state prison. The Massachusetts wiretapping law goes even further and makes it a crime to possess hidden equipment that is capable of making voice recordings. Mass.Gen.L. c. 272, § 99.
Hidden cameras as part of a home or office security system do not violate any laws. However, microphones are probably not lawful as they can record voices. Merely having microphones as part of a home security system can result in a criminal conviction. Of course, you can have microphones as part of the security system as long as you obtain permission from the person you are recording. You may be able to have the equivalent of permission by using signs that disclose the recordings. Such disclosures would probably defeat the purpose of having the microphones in the first place but would be adequate to prevent commission of a crime.
If you own or want to purchase a security system you should consult an attorney to find out what is permitted for recordings in your state.