If you really want to catch your other half off guard, the best way to do that is to hide the pregnancy test somewhere they're bound to check. Don't make it too obvious, and make sure you're there when they find it. Another important thing to note is that pregnancy tests only stay positive for up to 8 hours. After that, the results may start disappearing from the test.
Want your actions to do the talking for you? Just wear a T-Shirt! Custom printed t-shirts are a phenomenal idea to be subtle about it but still get the message across. You can wear something around the likes of "You're going to be a father." Or, if you don't want something so direct, you could go for "Bun in the Oven" to get the idea across. Whatever you write on the t-shirt, the reaction will be pretty surprising for your husband.