Alonso Scheme for PD is the best here. Thank you to all who have actually worked on and do some modification and updating. such as Qiaozhi Eteban and Morgan and other.
Good luck my friend Andreas. and I hope for you a good result in all the world.
the transmitteur and receiver 433MHZ and the right choice my friend. well you advance in this field. 433 MHz is used in the detection by the magnetometer.
Look this picture details and link
www.parallaxinc.com
If you need help for higtech you know my email.