Defensive devices in airline baggage
At US checkpoints, defensive devices do not share one baggage rule. Identify whether you have a chemical spray, an electrical device or a weighted striking tool. Then check the flight route and the airline's conditions before packing.
Self-defense sprays on US domestic flights
TSA keeps self-defense spray out of carry-on bags. FAA allows one qualifying container of up to 118 mL (4 fl oz) in checked baggage on a US domestic flight, provided it has a positive safety device. A spray with more than 2% CS or CN tear gas is prohibited. International aviation rules prohibit self-defense sprays in both bags, so do not carry the US domestic exception onto an international itinerary. FAA: sprays and repellents.
Stun guns and their batteries
TSA prohibits stun guns and Tasers in carry-on bags at US checkpoints. Checked carriage requires packing that prevents accidental discharge. If the device contains a lithium battery, check the separate FAA battery conditions and confirm the airline will accept the device. Possession laws at the destination are another question. TSA: complete item list.
Bear spray and weighted tools
TSA lists bear spray as prohibited in both bags; do not treat its canister as the small domestic self-defense spray allowance. A black jack is prohibited in carry-on but listed as permitted in checked baggage at US checkpoints. Secure its weighted end and check local possession rules separately. TSA: item list.