Human presence sensor?

[rtm]

Recall it from your memory.. when you are sitting in a motionless car, even if you are sitting with closed eyes, you surely can say when somebody come in (or go out) to the car - you feel it with changing center of the weight of all car.

Use L3GD20 ST MEMS motion sensor, it is 3-axis digital output gyroscope 3D sensor - the price is 2$.
&
LSM303DLHC, ST MEMS system-in-package featuring a 3D digital linear acceleration sensor and a 3D digital magnetic sensor - the price is near 2$ too.

You can see changing of car weight balance and starting/stopping of the car by using of these two sensors together. Also you can always read information about doors opening (and safety belt state) from CAN bus of the car.

So, the 4$ budget for the sensors and you can easily install it at any place of the car. Quod erat demonstrandum.

[Ichan]

Tire pressure change when standing still....you should see an LSB flip with a 6 bit converter, as an example

Nice, event i think this one will be difficult to fulfill the budget requirement as it will need a wireless transmission, still it is interesting - which sensor do you have in mind?

Use L3GD20 ST MEMS motion sensor, it is 3-axis digital output gyroscope 3D sensor - the price is 2$.
&
LSM303DLHC, ST MEMS system-in-package featuring a 3D digital linear acceleration sensor and a 3D digital magnetic sensor - the price is near 2$ too.

Another nice idea, will gyroscope has enough sensitivity for this? I have MPU-9250 somewhere in here - may try it.

I still have several months for this, any other tough please speak

-ichan