@gensay 

KD110 doesn't have a battery, so in general, it needs to wire to the existing doorbell to get power. Theoretically, if the input power of the device can be met, it can be installed and used in an environment without a doorbell system.

Frequently Asked Questions about Kasa Smart Doorbell (KD110)

Q1. Does kasa doorbell require an existing doorbell to be installed? What type of transformer do I need？

Yes, Kasa doorbell needs to wire to your existing doorbell to get power, it requires your doorbell wiring coming with a transformer that provides 16-24VAC and minimum 10VA output power, which is commonly used in house doorbell systems.