hi
if you straightners are "pug in" electrical ones then they are fine to carry in your hand luggage.
If you have gas ones then offically you are allowed to carry them with 1 x gas tube in them, any extra tudes must be MUST be oack in you hold luggage.
i have opersonally cariied gas straightner with me on a flight and the airline staff were not to happy so if you can avaiod this then pleae do as they will take "extra" notice to all other items you carry with you and it can take an awful long time to get through security!!!!!!!