The breathalyzers I purchased were good. I had a little trouble at first with a "error message". Then I decided to drink and wait for about 45 minutes then tried it again and it finally worked. Lol. Advice...drink some alcohol so you can get a reading.
Think it's important to remember that you need to wait a period of time before using the breathalyzer after your last sip, otherwise it over reports your level.
I purchased this couple of months ago and use it every time I'm out and have a drink or two. I purchased additional mouthpieces which come individually wrapped and I have shared with friends and allow them to use my machine.