When making a simple self-defense device, the first things to consider are safety, legality, and effectiveness. Here are some suggestions for self-defense devices that can be made using simple tools: 1. **Keychain weapon**: - Materials: key, strong rope or elastic rope. - Production: Fix the key to one end of the rope and tie the other end to your wrist. When in danger, the key can be used as a striking tool. 2. **Flashlight**: - Materials: a sturdy flashlight. - Usage: The weight and hardness of the flashlight can be used as a striking tool. And the flashlight can be used to illuminate or flash the opponent's eyes. 3. **Homemade spray**: - Materials: a small spray bottle, pepper spray or vinegar. - Production: Put pepper spray or vinegar in a spray bottle and spray it on the attacker's face, especially the eye area, in a dangerous situation. But you need to pay attention to the wind direction to avoid accidentally hurting yourself. 4. **Magazine or newspaper stick**: - Materials: magazines or newspapers, tape. - Production: Roll up thick magazines or several stacks of newspapers and secure them with tape. It can be used as a temporary striking tool. 5. **Pencil or pen**: - Purpose: Choose a sturdy pencil or pen, which can be used as a short self-defense tool for close-range defense when the threat is approaching. 6. **Mobile phone**: - Purpose: The mobile phone can not only make emergency calls at any time, but also be used as a temporary striking tool due to its weight and hard edge. In any case, the use of self-defense devices should be in accordance with the law and the purpose of use must be clear only to protect your own safety. In addition, in dangerous situations, even if you have a self-defense device, running away or asking for help is still the first choice. Regular participation in self-defense courses can also help improve self-defense skills.