Arduino project for Angle Sensor

The Aim
A device to operate an alarm when a vehicle is on a slight slope that may be at too small an angle to detect by eye. Device will be mounted on the vehicle, and is intended to warn the driver if he’s driving on a slope, who’s angle is greater than a certain limit.

Design Goals
Must be capable of detecting angles to an accuracy of 0.1 degree, and in one axis only - it should be much less sensitive to changes in the other axes, and also not be triggered by acceleration or speed. For avoidance of doubt… if the vehicle accelerates or decelerates, the alarm must NOT trigger. The device must only respond to angle.

The device must trigger an alarm when the ANGLE of inclination exceeds a programmable figure for more than a programmable period of TIME. ANGLE and TIME need to be easily changeable by editing the code.

The device should be “self zeroing” so that if it is not horizontal at switch on, it’s current angle is recorded, and measurements are taken from this reference.

As a guide to the accuracy/sensitivity of the device, a slope of 0.5 degree should NOT generate an alarm, whereas a slope of 1 degree SHOULD trigger the alarm.

The Job
The job is to recommend an inexpensive and readily available sensor array that will connect to an Arduino, to write a sketch to achieve the goals above, and produce a prototype that works reliably, and can be the basis for me to build several similar units.