舊身分證用唔用到

The answer is no.

The smart chip on your HKID will allow the Immigration Department to validate if the HKID is valid or not.

In this case, here is what you should do.

1. If you have reported to the police, you will need to bring that old HKID to cancel the report.

2. Return the old HKID to the Immigration Department for cancellation. HKID is not your property, but the Immigration Department. You must surrender your old HKID upon recovery in case of loss.

如已報失並領了新證，入境處已將舊證注銷；如繼續使用舊證過關，會給自己帶來不必要的麻煩；

2015-08-02 20:51:11 補充：
《人事登記條例》，任何人無合理辯解而申請或取得超過一張身份證，即屬犯法，最高可判入獄兩年。