person detection

My grandpa has had stuff stolen from his lawn recently so we are making a system that detects someone then sounds a loud siren, turns on a floodlight, and starts recording on a camera. I can't decide how to trigger it though, as it will be outside and I do not want an animal setting it off. I need some advice.
EDIT: Can someone also help me with the recording part?

People are generally, two legged animals. Perhaps you need to count legs.

Paul

Or you could get one of these (we have one).

The siren is not automatic. You have to look at the camera image on your phone when it notifies you
and decide whether to trigger the siren. There is also a microphone and speaker so you can interrogate
the 'suspect'.

We would like it to be triggered automatically - it is hard to wake my grandpa up, and I do not want him getting woken up because of animals. It would also be at night, as thats when his stuff has got stolen.

I am thinking a PIR with medium to low sensitivity, but what if the person is bundled up? And would animals still trigger it?

would animals still trigger it?

A PIR sensor is not going to distinguish between a possum or racoon and a person.

I am doing lasers and laser sensors 4 feet off the ground. I will also do a week of testing where it writes the data to an sd card.

raschemmel:
A PIR sensor is not going to distinguish between a possum or racoon and a person.

Mounting it high up is going to allow the sensitivity to small animals to be much less, if the
trigger level is adjustable you may well be able to set up a sensitivity that discriminates between
small animal and human, but the range might be more limited.

However there's no magic way to avoid false-positives I'm afraid with heat radiation detection.
Limiting the field of view to above the ground might be of use.

You could combine with a beam-break sensor at a suitable height too, multiple sensor types tend not
to have false-positives simultaneously.

I’d start of with a few microwave motion detectors around a perimeter; no motion no need to begin detecting. Once the perimeter detection is set up and running, I’d use some type of IR detection. I’d use a few SparkFun Grid-Eye Infrared Array Breakout - AMG8833 mounted to a rotation device to detect humans.

Some experimentation with the SparkFun Grid-Eye Infrared Array Breakout - AMG8833, using a dog and a human would give me an idea of how to discriminate between the 2.

What kind of microwave detectors? The little cheap one's don't work well outdoors, they rely on a complex pattern of reflected waves being disturbed. True radar sensors do work though.

I suggest you are approaching this from the wrong direction. Instead of trying to detect a person in the garden, which is obviously proving a problem, instead leave some things in the garden that low cost, visible and easy to steal. Put sensors on these so that when they picked up they trigger the alarm, cameras, lights or whatever. You might also do something like fitting a door (shed, whatever) with a second lock wired to the alarm and leave the key for that lock somewhere easy to find, such as under a brick next to the door.

A motion activated security light might be effective for your situation. If you are in the US Harbor Freight has a motion detector ans alarm for $10 when on sale. You might limit its lower field of detection to exclude animals. The "Ring" style of video cameras might also be effective, some may have features to distinguish between animals and people based on size and position. A DIY person detector probably isn't going to happen. This has been discussed on the forum for at least a decade.