He uses it to determine if someone/somewhat can overhear the conversation. Some sort of geigercounter, I guess.

I advocate the theory that he isn't hard of hearing at all. He uses the hearing aid to listen to frequencies that reveal paranormal activities. 

Albert: What kind is it? <referencing the wine>

Gordon: It's 11:05.

Albert: . . . <manages to not roll his eyes; knows Gordon's full of shit but loves him anyway>

This device has a blue light as well, and I think it was the same thing he used after first seeing Mr. C to find a 'bug' on Tammy and send her to the restaurant.  Cole uses this when he is visibly shaken from something and asks that no one make quick or 'sharp noises' or speech which will be like a 'knife in his brain'; first he was shaken by seeing Mr. C, and now by his encounter with the 'homeless squat' and the vortex. 

Also, this is device related to the idea of getting rid of bugs or 'tracking devices' which Mr. C did with his phone app after escaping from prison in episode 8.  The blue light may indicate that the device is searching for some source of sadness or problem(tracking device) which it identifies; but problems emerge when looking at how Mr. C and Cole approach and use this device, they think identifying the problem is the same as eliminating it, thereby avoiding the hard work of taking it seriously.  But we see with Mr. C that this is all to quick of a fix and this approach ends up with a false sense of complacency that allows the user to continue on, pretending as if everything is normal, that they can continue without going through the hard work of fixing the problem which of course will not be happy work.  The device allows a false sense of safety, happiness, and complacency, thereby effectively allowing the user to hide from the problems of the situation, this 'quick fix' device opens up the user of such a device to the full impact of the  problem which cannot be eliminated with an iphone or some sort of quick 'scanning', these 'blue' problems causing sadness etc., these 'tracking devices', are still there in tact.   Mr. C was complacent saying 'that should do it' after using his phone app, thereby thinking he had full control over the situation and could just take from it as he pleases(get all of the coordinates, kill Ray, etc.) and it is precisely then that he is 'tricked', underestimating the problem in front of him, that Ray may have planned as well and worked with the warden, Mr. C then confronts Ray at the wrong time, who was better prepared for the situation.  

Finally we have Cole, and this episode shows that although he is played by Lynch, he is by no means a perfect or guaranteed savior, people have problems(and this is a huge revelation apparently, things are not always alright, nor should bad things have to be tortured and mutilated out of all rationality to pretend that everything is alright and hide, this is the pre-Cooper Dougie mentality and why Mr. C created Dougie to hide his crimes).....The other part where Cole was having wine while talking to Albert over the phone, who was about to meet Diane for the first time, was the first hint that problems were emerging around Cole and Albert.....Cole needs Albert and his skepticism of 'small town'/backwards ways, etc., to keep him from getting too immersed and getting close to the Dougie path(Dougie is too immersed and is easily controlled, while Mr. C is too detached and externally drains the situation; Cole gets too immersed, while Albert is more detached, etc.).  Cole and the 'quick woman' here is like Dougie and Jade.  Cole was shaken by the 'homeless squat', it is making his hand shake, and wants to quickly eliminate the 'knife in his brain' and return to 'happy', thereby using the device's blue light to scan for sadness/problems, but it is apparent that like Audrey's search for a quick fix, or Trick with the shaking hand at the bar, that this approach leads to disaster, the 'spreading it around' and the 'quick fixes' damages Audrey from what she was into what she is now and is on the verge of driving the daters mad and getting Trick into serious trouble for breaking house arrest, nearly getting killed, while the women at the table are saying, hes here 'whoopee'.  Cole's quick fix here is immediately going to lead to bigger problems, immediately after he scans, he says to Albert 'you are going to be the one to tell her', or break the bad news to the woman he seduces then dumps once he realizes it was a mistake, who could 'go mad' or be hurt from the situation.  Also, Cole begins to take his duty as FBI as a joke precisely when he is taking his relations with the woman as something only quick and fun with no consequences, as if it is a magical cartoon where everything will disappear the next day(problem with the people at the roadhouse and what is destroying Audrey in her psyche), at this same time Cole makes light of his duty as an FBI agent, pushed work off onto Albert like before in Philadelphia when Albert had to meet Diane, then yelled at Cole the next day, now Cole is making fun of the missing girl with the turnip joke, thinking the 'raid' where they get someone in a 'trap' is funny and not serious business.  Finally, Albert then steps in to question his judgment, saying look 'are you sure this is good, this wine'..... what about 'day after', what about our work, etc......?