Why the location add-on is billed on its own

One place is $4.99 a month, charged every month.

Everything else on your plan renews together on one date. The one-place alert is sold by the month, so it cannot sit on that same bill. When you add it, it gets a plan of its own: charged each month to the card you already paid with, with its own invoice. You do not type your card again; if your bank asks for an extra check, press Finish paying on Billing. See My bank asked for an extra check.

Up to 10 places is $3.33 a month.

The up-to-10-places size joins the plan you already pay for, on the same bill, when that plan is sold on the same schedule; if it is not, it too gets a plan of its own.

Removing it

Because the one-place alert is a plan of its own, Remove does not stop it at once: it stays on until the end of the month you have paid for, then stops, and nothing more is charged. Press Keep it before then if you change your mind. See Removing an add-on.