Free shipping where available. At the same time, we continue to work toward replicating the success we've had with ISOD overseas here in the US by expanding its availability beyond our current network of roughly 620 CPR stores and ZAGG franchise locations.But without caronvirus, I will tell you the first half we've got some good line of sight to our possibilities of distribution.
Please go ahead, sir.While we don't typically provide quarterly guidance, given the number of moving parts and that we're more than two-thirds the way through the first quarter, we wanted to share some specific details to help you understand the change in our year-over-year performance.Yeah, for sure.
And then also what are your thoughts from a -- does that also mean forecasting in potentially soft demand for some of the geographies that have been hit harder? But is there a -- do you think that long term you'll diversify your supply chain to be less dependent on China?Innovation will continue to drive the business forward in 2020 as we have a great product pipeline that will further enhance the consumer experience and allow us to maintain and grow price points at retail.As it relates to the outbreak of coronavirus, it's obviously a very fluid situation that we continue to monitor closely.
ZAGG assumes no obligation to revise any forward-looking statements that may be made in today's press release or call.Thank you. We have taken safety of our employees and our partners as top priority. We expect a year-over-year decrease in total opex expense and improvements in inventory terms.To help drive sales, we increased our advertising spend and ran incremental promotions with several major accounts.
So as part of inventory any freight and duties that you used or that you pay to bring the inventory to your location and prepare it to sell gets capitalized into your inventory. I think what we've done from a segmentation perspective has really helped to solidify our market share.
I think for InvisibleShield you had the last year was about protecting consumers from harmful blue light. Lot of impact from less retailers going -- or less consumers buying in retail.Okay. In the event we receive future transaction interest, the Board would welcome the opportunity to evaluate any transactions that can maximize stockholder value.Thank you for taking my question, Chris.We're seeing some softening in other areas as well. Your line is now open.With that, we will now open up the call for questions.Our three acquisitions Gear4, HALO and BRAVEN, which we acquired in late 2018 and early '19 respectively, contributed approximately $83 million in revenue in 2019, up over 20% over 2018 levels. We're projecting Q1 adjusted EBITDA to improve to negative mid to low single digit range, compared to negative $9 million in the first quarter last year with further improvement in the second quarter versus the prior-year period.Internationally our screen protection business is enjoying great momentum driven by the success of our use of this strategy in which we invested heavily during 2019. So for us the key is to continue to drive cost down of the product, but also develop a product with tariffs in mind.
In terms of our performance versus expectations, full year revenue came in just below the low end of our guidance range, while adjusted EBITDA fell short of our projections.While it is the smallest of our three acquisitions, BRAVEN had a busy Q4 adding 1,100 new doors. Our objective is to exceed this target and we look forward to updating you on the progress, especially as we get a better understanding of the impact of coronavirus and visibility into the rollout and adoption of 5G become clear in the second half of the year.Gross margins are currently estimated to be in the mid 30%s as a percent of sales, roughly flat compared to 2019.
Gross profit as a percentage of net sales remained flat, but we saw upside from an increase in sales of Gear4 cases and HALO power products. Not only does it look great in any environment, the stiff rubber overmold absorbs impact and can withstand drops up to one meter.