Interestingly alcohol itself doesn't have any carbs, since the carbs (sugars) have turned into alcohol and so are no longer carbs. So if you have a Vodka and Diet coke for example, there are no carbs at all in it only alcohol, which in itself contains calories. A single measure being about 55 calories.
The annoying part is that the body burns alcohol ahead of fat, like it does with carbs. So you stall your weight loss (momentarily) for about 20 mins whilst it burns that alcohol off with normal activities such as breathing, and then returns to fat burning, assuming you've had no carbs.
Vodka and Diet Coke and Gin and Slimline tonic/bitter lemon have about the same calories at 55 per single measure. The mixers have none.