That’s actually a pretty good question. Good quality wireless earpieces are available, affordable and would be far more inconspicuous than the classic ‘wired’ models. So why don’t the secret service make their presence a little more, well, secret?
The main reason is largely psychological in nature (though there will be a technical component later on). You see, if a potential troublemaker looks into a crowd and sees nobody there that he/she identifies with as a threat, then said troublemaker will be far more likely to start making trouble. However, if they notice secret service guys using their trademark earpieces, then they might think twice about it and a lot of unpleasantness can actually be avoided.
To you or I (assuming that you aren’t a troublemaker?), the secret service guys are just that, they usually appear to protect someone or something, so we ought to have no reason to fear them. Ergo, they stand out just enough to deter the would-be troublemakers, but not so much that they frighten the rest of us or distract from whatever proceedings we happen to be, um, proceeding with.
If you’re sitting there saying, “hang on, what happens if they want to sneak up on someone?” then my answer is still the same, expect that I would imagine that the secret service would put two or three agents within visual distance of a suspect and then ‘herd’ the troublemaker towards other agents in the vicinity. I have no evidence (or experience, I’m grateful to say), to back that up, but it seems reasonable to me to do it that way.
Now, onto the technical part: wireless communication, whilst it has improved greatly in the last few years, is still not as reliable as the more old fashioned forms of ‘wired’ communication. Wireless communication can be subject to signal interference, as well as suffering from a more limited bandwidth.
Finally, wireless communications gobble up battery power far more than their wired counterparts, so for tasks that may last for several long hours at a time, long battery life is a must.
When the wireless technology improves, I suspect that the secret service will make the leap, but I also suspect that they’ll keep the coil, for the reasons stated above.
Also, as an added extra – if you’re wondering why they touch their ears when they receive a message (much to my fellow Brit James Bond’s chagrin), well, that’s because pushing the earpiece into your ear drowns out background noise and also makes the message louder. They simply do it for sound clarity when receiving important information.