GPS devices and their constant demands can at times actually sound like the machines are nagging or being bossy. Tech researchers are trying to make the voices sound less robotic, but they're facing hurdles, according to CNN.

For GPS devices, voice technologists record human actors reading different sentences. Computers store these sentences in a database, chop them into sounds, and then remix them to make any possible combination of words. The result is intelligible, but it's not quite human.

One reason for this is that human speech is complex, with about 40 basic sounds in the English language, with seemingly limitless combinations. But this will improve as computers continue to get faster and are able to store more data, said Mark Gretton, chief technology officer of TomTom, a GPS maker. Also, technology appears to have made some strides in replicating the sound of human emotion and inflection.

To make computers sound more human, the machines must somewhat understand what they're reading so that they know when to inflect. This part of computer science is much more challenging, said Andy Aaron, a computer speech researcher at IBM.

The user's mood at the time he is using the technology is another factor. How well a computer voice matches the listener's mood is not just a matter of preference, it's a matter of safety, said Clifford Nass, a Stanford professor who studies computer voices.

A study found that these emotional mismatches may actually be dangerous in driving situations. Sad drivers who get instructions from happy computer voices, and happy drivers who listen to sad voices, are more likely to have accidents, he said. The emotionally confused drivers are also less likely to be able to pay attention to the road.

One solution gives drivers options when it comes to the voices of their computerized companions. TomTom offers a range of downloadable voices, from the fictional Darth Vader and Homer Simpson to celebrities like the rapper Snoop Dogg. Users can also read a list of test sentences and have their own voices transferred into the GPS.