It does not matter garage or house. If you turn it on when you are there, if you're in a one party state, you're good. If you are in a two party state, could get you in trouble. You'd need to weigh the cost/benefit in a two party state, as well as know that if there is no big benefit (like keeping you out of jail on a DV charge), the recordings should never be even discussed with anyone. They did not occur.
But recording of people while you are not there, without their permission, generally is very frowned upon as it is illegal.
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hoosier_dad makes a really important distinction. Most of the "one party vs. two party state" discussions that you'll read on this forum and elsewhere on the internet have their roots in both federal and state _wiretapping_ laws. The applicable laws can be _very_ different with regard to video recording. Especially when it comes to video recording when you are not present.
In general, when it comes to video records, no audio is better than audio. Video monitoring in locations where there should be "no reasonable expectation of privacy" is better -- but not always legal -- than video monitoring places that could be expected to be private. For example, video records of what is going on outside your house on the public sidewalk and street may be treated very differently from video records of a bedroom, a bathroom, or even a den/living room that could be expected to become private with the closing of the drapes.
Please be very careful. Do not assume that laws that apply only to audio recordings apply equally well to video recordings. In some states, I believe they could even come after you with various "stalking"-related statutes as well as both civil and criminal "invasion of privacy" actions (just in case you were not aware of that possibility).
You'll need one "Master System" camera that plugs into power and network. Then each additional camera ($199-$299) just plug into power (Ethernet over Power networking - not wireless).
All of the solutions above have movement alerts (like sending you an email) and options to only record when movement is seen (logitecs lets you select where it will look). They also all have free iOS app, Android app & Web interfaces that can control multiple cameras.
Now for the legality of it. If no one is legally permitted in this particular location, then isn't it ok to leave a camera running there? Or would recording a trespasser actually be illegal?
I had to check on this for Michigan because I recorded audio and video in and around my shop. The only requirement was a notice (stickers) on the doors that this was taking place. That provides constructive (legal) notice. I think the same goes for private homes also, especially your own home when it can be shown to be part of a security plan.
Foscam makes some decent wireless (with wired port if you prefer) cams that you can remote control, watch from your fone, internet, etc. I have a couple around my home. Two way sound, 180 degree movement, IR nightvision. I think it was some $80.
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