Have used the original Pawtrack.com, whilst the concept was good - the collar was massive and the battery life was a bit flaky - the wolf lost his twice. The first time they managed to turn on a beeper and we located it, the second time it went forever as the battery was too low (30%) for it to work - they offered a discounted replacement, but I couldn't risk him losing it again. The support from the guys behind it was second to none though, and I know they've listened to their users and made improvements. It's now however way too pricey for me to consider. I originally paid around £80. It's now more than double that.