Mobile sound machines typically offer three power approaches: replaceable AA batteries; built‑in rechargeable lithium‑ion batteries charged via USB; and plug‑in AC (electric) power. Some models combine USB recharge with replaceable batteries, while others are electric‑only.
Most mobile sound machines use plastic housings—commonly listed as general “plastic” or specifically ABS (Acrylonitrile Butadiene Styrene).
Many units include a soft built‑in night light with adjustable brightness (examples show warm amber dimmable lights and models with three glow/brightness levels). A few devices list multiple color options—one product mentions a 7‑color light.
Product details list child locks, BPA‑free and phthalate‑free materials, reinforced clips or rings for secure attachment, drop‑proof/drool‑friendly designs on some portable units, and simple one‑hand or user‑friendly controls.