This is a light stick from the Saudi Arabian National Day concert at the Osaka-Kansai Expo. It was used only during the concert. Pressing the black button cycles through the following modes: flashing green rapidly → flashing green → solid green → off. There's a magnet on the end of the black part, allowing you to form a loop. It seems like the battery can be replaced (see photo 5). It has been lightly wiped with alcohol. Instant purchase OK. No pets, no smokers.