How To Prove Tenant Smoked

[John E Ceisel]

Hello BP!  

I own/manage real estate in San Diego, California.  I have a condo where my lease agreement clearly states no smoking.  I went into the unit twice in the past couple weeks for showings and both times it had a strong odor of cigarettes.  Knowing the tenant smokes, I asked if he smoked in-unit and he denied it.  I confronted him the second time and he says he is burning incense.  Needless to say, incense does not smell like cigarettes. 

Is there a way (legally) to prove he is smoking in-unit (other than logging the offenses)?  I am going to have to pay for remediation in a month when he moves out and I'm concerned he will continue to deny in-unit smoking and fight me on security deposit deductions.

I found a kit online that tests for nicotine residue.  Will this hold up if I need it?  Appreciate any insight you guys have.