Quickly test your BAC levels with this BACtrack BT-M5 mobile breathalyzer, which is compatible with most Bluetooth-enabled iPhone and Android 4.3 or later smartphones and features police-grade Xtend sensor technology to ensure accurate readings.
VERY accurate when used correctly, by the instructions and with common sense. Upon reading the privacy policy included in the packaging, the cloud sharing capability does raise concerns over personal privacy, user data security and 3rd party sharing, among other things. Used in "anonymous" mode (default) I have found it to be VERY accurate.
The CNET review of this product is spot on and is a worth it read. I hope this review helps you make an informed decision and PLEASE KNOW YOUR LIMITATIONS AND DO NOT DRINK AND DRIVE.