Accelerometers used to be expensive devices in aircraft and missiles, but now they are very cheap devices found everywhere — for example, in your mobile phone. Their use in a mobile phone is not as critical as part of an aircraft navigation system, and the accuracy and cost reflect that, with 3-axis devices costing less than a dollar, even in small quantities. Due to MEMS (Micro-Electro-Mechanical Systems), you can now buy low-cost accelerometers made directly on Silicon, so using the low-cost manufacturing facilities used for making normal integrated circuits (with some modifications).

Before MEMS, there were several ways of making an accelerometer, but they tended to use the same principle – a proof mass attached to a support, and its effect on that support is measured, for example, with a strain gauge. Such a structure will be resonant so they need a damping system. Also, gravity will produce a continuous 1g (9.81m/s) acceleration in one direction, which is why accelerometers always have a full-scale range of 1g or more. MEMS accelerometers are similar and work by having a small proof mass displacing a micro-machined structure, and movement is often measured by capacitive means. The devices have internal damping from the air trapped in the IC cavity or a fluid could be used.
The Analog Devices ADXL50 is shown below.

An analog accelerometer will simply have a voltage output, such as the NXP FXLN83xx.

You must add capacitance to the outputs to filter them (see datasheets for details).

Digital accelerometers are more common and cheaper, such as the STMicroelectronics LIS3DE, which is only $0.62. It even has an auxiliary 10-bit 3-channel ADC, but the accelerometer data is only 8-bit. A 16-bit version would cost around $1.10 and doesn’t have the auxiliary ADC. You will typically have an SPI or I2C interface.

When choosing a digital accelerometer, you need to bear in mind the different resolutions available (from 8 bits to 16 bits) and the zero g offset, which can be quite significant. For example, 0.1 g is 5% of full scale on a 2g accelerometer. Even 16-bit accelerometers can have a significant zero offset, amounting to maybe 40 LSB (least significant bit) counts.
Some devices have a high-pass filter that can remove any offset, but at the expense of not being able to measure steady acceleration. You will not detect static gravity and hence orientation, only changes in acceleration, so the use of high-pass filters is limited to a few applications.

Typical bandwidths will typically be 1kHz or so and can be unequal, so you might have a lower bandwidth on one axis (typically the Z-axis). However, for the typical use of accelerometers such as monitoring human movement, the bandwidth is unlikely to be a limiting factor. You will be more concerned about the response time with an airbag sensor because you cannot wait half a second for an airbag to trigger. Still, again, the bandwidth shouldn’t be an issue because you would be choosing a device certified for safety-critical automotive applications if you were designing an airbag trigger, so that would restrict your choice to devices that will also have a suitable bandwidth/speed.

These images are of the Analog Devices ADXL202 in their Analog Dialogue article “Using MEMS Accelerometers as Acoustic Pickups in Musical Instruments,” which also has some other useful information about the structure of MEMS accelerometers. It shows the sensing element in the sensor and the processing and interface electronics around it.

Accelerometers typically have a 10000g shock survivability, and if they are packaged in plastic, they are molded with a protective cavity to allow the sensor to move slightly and avoid contact between the plastic and the sensing element.

So, what would you use accelerometers for? You probably already have a couple or more in your possession — one in your car’s airbag and another in your smartphone or tablet — to change the display orientation when you rotate the device. They can also be used on pedometers, gaming (such as Wii) or virtual reality devices; as an input device in place of piezo where the input device is tapped or struck; vibration monitoring for industrial applications; motion detection for power saving in electronics devices and automatic wake-up; seismology; navigation; free fall detection to protect disk drives; car stability control; image stabilization and orientation detection in cameras, and drone stabilization. They seem everywhere and are low-cost when considering the complex technology involved. It opens up the possibility of new applications that haven’t been considered before. Also, their use in consumer products, in particular smartphones, tablets, and cars, has really helped to bring the price down from something that would have been a very expensive part 20 years ago. They are simple to use with low power, low voltage operation, and digital interfaces. In the past, accelerometers were large, heavy devices that could not have found their way into a smartphone. There are numerous manufacturers — simply look at one of the main distributors to find NXP, Analog Devices, STMicroelectronics, Murata, Bosch, Epson etc.
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