An active or aggressive alert occurs when a dog responds with a vocal or otherwise overt reaction to locating drugs. An active alert might be barking, straining toward, digging, or pawing at the spot where the drugs are located.

Detection dogs are trained to provide one of two types of "alerts" when they identify the scent of a controlled substance: passive or active. Most modern drug dogs, especially those working in crowded public spaces like airports or festivals, are trained for a "passive alert." In this scenario, the dog will simply sit or lie down next to the source of the scent and stare intensely at it. This method is preferred because it is non-disruptive and does not damage property or frighten the person being searched. An "active alert," which is more common in outdoor searches or older training methods, involves the dog barking, scratching, or pawing at the location where the scent is strongest. Once a dog alerts, the handler rewards them with a high-value toy (like a tennis ball or a tug toy) rather than food, as the "hunt" is seen as a game to the animal. It is a common misconception that drug dogs are "addicted" to the substances they find; in reality, they are strictly motivated by the play-based reward they receive from their handler for successfully completing their "job."