For one thing, GPS doesn't work indoors, and for another, they don't make devices quite this small, especially when those devices have to relay their measurements back over a network.
问题之一就是，GPS不能在室内工作。 还有一个问题，就是他们造不出这么小的仪器， 特别是当这些仪器需要依靠 后方网络的测量时。