This portable baby monitor is powered by the built-in rechargeable battery or standard household current. Sony Baby Call Nursery Monitor: * Sony 900MHz monitor has five sound-sensor activity lights, out-of-range indicator and low-battery warning keep you informed of your baby"s actions and the status of your equipment * A belt-clip is included for both receivers, keeping your hands free for other activities * Receivers are water-resistant for use in the bathroom or kitchen * 900 MHz technology: extends the range to let you take the receivers farther from the nursery, yet still hear activities in the nursery * 27 channels to greatly minimize interference: uses FM transmission system with channel selector to locate the clearest channel, helping to eliminate interference for clearer communication * Built-in rechargeable battery receiver: provides great savings and convenience over replaceable batteries * Voice activation mode: eliminates most extraneous background noise for clearer transmission * Sony baby monitor model: NTM-910YLW