Hi,
@Kellya , one other thing to try is to shave the bit of your arm it's being stuck to.
Even if someone doesn't have hairy arms, there's usually a sort of fine "peach fuzz". Uncovered, those hairs will get knocked off, but covered with the sensor, they can grow a fair bit and don't help the sensor stick.
So, best to run a razor over it first so it's being put on a totally smooth area.
Use the alcohol wipes too and give it a few minutes to dry really well.
A lot of new users don't realise at first how many times they tend to bump into doorjambs, or drag their coatsleeves, rucksacks etc across their arm, all of which might tend to snag the sensor and loosen it, so after a while, we tend to develop a "spatial awareness" to lessen bumping it.
Also, new users sometimes place it on the side of the arm where it's more likely to be knocked, so getting into the habit of placing it further round the back of the arm makes sense.
Molnlycke Mepore 7 by 8cm plasters, about 17p from Boots are good for smoothing out the edges against snagging.