Invisible ink 🔵 After writing, the ink will be invisible, unless you turn on the light on the cap to see the secret information perfectly. | Safety 🔵 your child's healthy toy! Suitable for T-shirts, paper, skin and any smooth, faded ink surface, permanent but washable! | The perfect gift 🔵 suitable for children's birthday gifts, holiday gifts, children will be very happy | Warm reminder 🔵 children under 3 years old do not use, the product contains small parts! ! ! | Accessories 🔵 our pen comes with a battery, no need to purchase additional batteries, the insulating sheet between the batteries can ensure that the electric pen you receive is fully charged