Sensor to detect presence of an animal under a vehicle

My project is basically to detect dogs or cats that take shelter under the car. Since, it is huge problem in places that have stray dogs and cats, people usually don’t look under their vehicle before getting in to drive and these animals die as people drive over them.
So I want to know what king of sensors should I use to detect the presence of these animals.
I though of using thermal camera but they are very expensive.
Please help

PIR sensor is one possibility. But, limiting the range might be difficult, as it will tend to detect heat changes beyond the underside of the vehicle. One way to mitigate this is to angle the sensors down, so they're looking at the ground, before they see beyond the vehicle's perimeter.

The PIR sensor will do a good job of detecting the animal as it arrives. But, once it settles, and stops moving, the sensor will no longer trip. So, a means will be needed to capture these events, and hold them until they are cleared. An Arduino could easily do this.

Another problem might be heat coming off things like the vehicle's exhaust pipe, muffler, catalytic converter, transmission, and from the engine compartment. So, this might only be effective after the car cools down.

Another possibility is low-to-the-ground laser beams, with a sensor that trips if a beam is broken. Low power IR lasers would probably be best, so no eye damage occurs. But, not sure how the lasers would be mounted/positioned and such.

Another possibility is a large pneumatic bladder, with a pressure switch. If a dog or cat walks on it, or lays on it, the pressure will increase, setting off the pressure sensor. Not sure where you would get such a thing. Back in the old days, when "service stations" truly provided service, a pneumatic hose would cause a bell to ring, whenever a car rolled over it. The bladder would be the same idea, only more sensitive.

Similar to the bladder, a mat with flex sensors. A foam mat would deform when a cat or dog laid on it. If it was striped with flex sensors, that would detect their presence. Again, not sure where you would get such a thing, but it might not be too hard to make. Also, not sure if it would be sensitive enough to sense cats, or small dogs.

And, how about a shocker grid. If they step on it, or lay on it, a mild shock encourages them to move on.

Or, maybe something crazy like tiger piss, sprayed on the pavement, under the vehicle. I have no idea if that would work, or how long it would last, but worth a mention?

Or, an MP3 module with a "Did you check under the car?" recorded message that plays when the ignition is turned on. Or a magnetic reminder sign on the driver-side door, or a tennis ball that hangs from the vehicle's ceiling and bonks the driver, reminding them to look.

Marten and other rodent repellers systems are already available for cars.
They work with bursts of loud ultrasound, which also might scare away dogs and cats.

Same principle as the “Mosquito alarm”, to chase teenagers away.
Leo…

Unless the OP has a 4x4 truck or something, most teenagers won't be able to get under the vehicle, especially as so many of them are overweight these days. So just the skinny ones to worry about.

I though of using thermal camera but they are very expensive.

This 8x8 thermal camera is not expensive.

jremington: This 8x8 thermal camera is not expensive.

Somewhere around $50? Same price as a Raspberry Pi.

At that price I am not going to get one just to play with, tempting though it be!

$39.95 plus shipping. Roughly, ten cups of cappuccino.

Thing is, I don't drink coffee, and I am not in America. :roll_eyes:

Is that even a problem? I thought most cats and dogs are a tad smarter than that, and will run out the moment the car starts moving due to the driver getting in, then the noise of the slamming doors, and finally the engine starting.

Also such animals have to really align themselves well with the wheels to be hurt, if they sit in the middle (a more sensible place to begin with) their shelter will generally just move away from them...

The cat sat on the mat.