The use of breathalyzers you can buy online or in stores are not a reliable source indicating whether or not you have had too much to drink.  

These machines are simply not accurate even when given by police who are trained to use them and have any many source of error.  The only thing they may be possible trusted to do is the potentially give you an indication of whether there is alcohol in your system. Not sure what that is worth with anything, but do not ever make any decisions based on giving your self that machine.  Just like a lawyer who is his own client has a fool for a client, same for a doctor and the same for someone giving themselves a breath test or treating themselves.  There  is no reliability.

Click here to read additional information about breathalyzers and their flaws.