Keychain Personal Alarm With Flashlight
https://www.storeboard.com/blogs/general/no-time-no-money-no-problem-how-you-can-get-keychain-alarm-with-flashlight-with-a-zerodollar-budget/3356923
After you have a receiver it can consider and approach signals from many products, This provides you the pliability to add devices later on with no cost of extra receivers.