A pH meter is a device that measures the acidity or alkalinity of a liquid. pH meters consist of a probe that is connected by a wire to a meter that gives you the readout of the pH. You can also measure the pH using test strips or pH indicator fluids, although there are advantages of using a pH meter.
While pH meters are a little more difficult to use because they must be calibrated and maintained, once they are properly calibrated, they measure more accurately than a test strip or other method of pH measurement. The number of hydrogen ions is quantified by the meter, which is essentially a voltimeter and is a lot more sensitive than other methods.
Ease of Use
Using a pH indicator can be messier than using a pH meter. Using a pH meter, you can insert the probe into the liquid you are measuring. Using an indicator requires you to remove an alloquot of liquid and place it into the measuring device to which you add chemicals.
Reading a pH meter is much less subjective than reading a color strip or a pH indicator. Color strips and indicators can give a range of colors and be subject to being read differently by different observers and are completely limiting for color-blind individuals.
pH meters are much more precise than other methods of pH measurement and are able to measure down to the 0.01th of pH unit. There are pH test strips that cover ranges smaller than 0 to 14 (e.g., 3-6) which can give a more accurate level of detail than standard strips, but these are still not as accurate as a pH meter.
pH meters offer the advantage of not being disposable. Aside from having to occasionally purchase calibration standards and probe storage solutions once you make the initial purchase, you can measure as many pH values as you desire. Each time you measure pH using another method, you will have to replenish your supply.