As other mentioned you need to check pressure in each tire, if one is low then most likely you have nail with slow leak, if all are the same then reset the sensor, probably temperature change caused drop in pressure. I need to add couple pounds every few months, aluminium rims are very hard to seal 100% and if there is no other problem, the rim itself could be leaking and that would be warranty repair I would think, but I'm not sure about nail or other road hazards.