These devices typically contain a cylinder of compressed nonflammable gas. Some models also contain a small explosive charge (squib) to release the cylinder contents.
For international flights check with your airline as international regulations may vary from domestic regulations.
Though not restricted as a hazardous material when the gas cylinder is empty and no explosive charge is present, airport security screeners may still want to examine the gas cylinder to ensure it is empty.
For models containing Li-batteries, see PackSafe battery guidance