Since points will expire when your account is inactive for 180 days, you will receive a reminder email before your points are set to expire so you have ample time to make a purchase.
Please know that you must be opted into emails for this reminder. To opt in for emails select 'More' at the bottom of the page and then 'General Settings', from here you will see the toggle switch for promotional emails. Be sure that this switch is turned to the right.