We present ATHOME, an Automatic Tunable wireless charging framework for smart low-power devices in current and future HOME. ATHOME automatically tunes the charging power of multiple stationary wireless chargers to provide enough energy that can continuously power up smart devices with varying working power profiles, while minimizing the total charging power to reduce energy cost. To reach this goal, ATHOME first solves a hard open problem of calculating the minimum required charging power for powering up a device with limited energy storage size and varying power profile. Based on the minimum charging power obtained for each device, ATHOME then provides an optimal solution with polynomial-time complexity that automatically tunes the charging power of all chargers in a real-time fashion, which enables all devices to work continuously while minimizing total charging power. We implement ATHOME on a WISP platform with 8 rechargeable nodes. Experiments demonstrate that ATHOME provides sufficient and tight charging power that enables devices to work continuously.