Originally Posted by bittetech

I shaved my trunk keyhole earlier this summer with the intention of using something like a keyfob to pop it. I relocated the key hole to the bottom of the trunk (inspiration from Hakuna miata) but re-hooked the trunk release line to the center console for convenience. The prices for conventional keyless entry boxes aren't terribly expensive - but I decided I hate carrying around a keyfob but I almost always have my phone.

Been working on this for a couple of days. It's not the most secure code in the world - but I doubt bluetooth man in the middle attacks to be too extremely common when you can just slash the top to break into a car. And, as an added bonus - it's actually cheaper than pretty much everything else.

I still need to optimize for power consumption to keep draw on the battery low - but I'll do that once the final parts from china arrive.

So - how much is this costing me? Ebay rules for stuff like this.
BOM:
$3 5v Arduino pro mini (from sparkfuns arduino days special)
$7 Bluetooth HC05 module
$8 8 channel relay driver (was going to design one, but for $8? not worth the effort)
$10 for 3 lock actuators. Fun fact - I pulled 3 from the junkyard at 8$ a piece. I ended up returning them when I found I could get them new for cheaper with hardware.
$3 door switch
$31 dollars

So how this'll work - come up to to the car, press button installed under the edge of decklid - arduino wakes up, queries bluetooth/phone presence, and unlocks trunk. I'll need to install a switch on the door handles somehow, but installing the actuators is already documented. I'll have 2 channels left over for relay stuff, just need to decide what I want to do with those (fuelpump cutout? interior lights?)