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On-Site Car Alarm Installation: Parnell or Hillsborough

Looking to get a car alarm installed on my 2010 Honda Insight on-site (while I'm at work or at home. Either Parnell during work hours and Hillsborough if scheduled for after hours or weekend. Would like to know where to start with car alarm installation. Would I need to buy the parts first or pay for both the car alarm parts and installation at once? Open for advice. (: Cheers!