RC transmitter alarm

Try measuring an the voltage in AC mode. It might not work because of the frequency response of your meter

Think of it as a fixed frequency speaker. e.g. https://www.murata.com/products/productdata/8801054523422/SPEC-PKM13EPYH4000-A0.pdf

If you need a scope, the DSO 150 is like $25.00 USD. https://www.banggood.com/Original-J...s-all-newcustom-ncv90-0623&ad_id=443948744865 It may or may not come with an AC adapter. I strapped a 9V battery holder on the back of it.

Hi all have ordered a scope and will get back to you all later when I have some results, or not as the case maybe thanks again all for your help and encouragement which for me a humble spanner man is a minefield.