Ultrasonic, no collar needed.
Range up to 30ft.

PetSafe Ultrasonic Pet Trainer

When the system emits its ultrasonic sound, your furry friend will understand that you want him to stop whatever he is doing. The system also has a positive tone to reward good behaviors as well as a negative tone to counter undesirable ones.

Features:

• Uses ultrasonic sound
• Range up to 30 feet
• Uses a positive tone for rewarding good behavior
• No receiver collar required