Initially, I felt a strong effect from the devices, but not anymore. Has the effect diminished?

No, over time, the body starts to accumulate the energy in a way that its own energy level becomes closer to that of the field emitted by the products. Once your own energy level has harmonized with that of the product, you may no longer perceive the field's strength. However, this does not mean that the effect has diminished. One could refer to this as becoming "accustomed" to the field.