请教加州关于dash cam使用的规定

水中捞月给了这个链接。看完后还是有些地方不明白。

http://www.ehow.com/info_12333580_legal-use-car-dash-camera-california.html

这里说：

A crash or "unusual motion” of the vehicle can automatically trigger the camera’s recording function, but the driver can also manually operate it for the purpose of monitoring his driving performance. The recorder may not store more than 30 seconds of data before and after the event that triggers its recording function.

这个30s before the event到底什么意思？如果recording function还没有被trigger，哪里来的data？

我在考虑买一款开车时就自动启动的dash cam，能记录24小时。到底合法吗？

所有跟帖： 

• Bad Writing -柠檬椰子汁- ♂ (656 bytes) () 01/18/2015 postreply 11:38:21

• 原文说法有语病，改写后依然存在。 -十年之前- ♀ (411 bytes) () 01/18/2015 postreply 11:58:59

• 语言要精确 -柠檬椰子汁- ♂ (411 bytes) () 01/18/2015 postreply 13:29:39

• 我猜recorder是这样的： -nj_guy- ♂ (281 bytes) () 01/18/2015 postreply 14:38:16