Dogtra T&B 2200
It has 2 different tones and you can run it in 3 different modes....
- silent (only beeps when dog is stopped)
- run (beeps every 8-9 seconds when dog is moving and every 2-3 seconds when stopped)
- manual (beeps only when you hit the 'locate' button)

I've had mine for 13 years, the internal battery in the handheld unit is finally not holding a charge as long as it used to. For $29 plus shipping, Dogtra will replace the battery for me.