Obviously the perfect headphones are necessary for rocking out solo, but you can’t have a Call Me Maybe office dance party with just a pair of earbuds! We’re big fans of pumping up the jams here at Brit & Co. But we’re not big fans of sucking the power from our already strapped devices or constantly changing batteries on crazy complex speaker systems.

So we searched for ways to rock out, powerlessly. When we found Amplifiear, the Kickstarter project that used low-tech sound amplification to boost our iPad volume, we were loving it. Our iPhones felt left out though, so we went on the hunt for the perfect way to improve their sound without taking away their precious battery life. These 6 “passive speakers” are great for jamming out, sans an external power source.

1. Eco-Amp ($8): Let’s start with the incredibly basic. This eco-friendly amp is made of recycled paper, shipped flat, and printed with soy-based inks so that your environmental impact is as low as possible. The amp can be assembled and then folded back up for easy transport, its big enough for a good jam sesh but small enough to be used virtually anywhere, and it comes with two so you can always have magnified music at your fingertips.

2. Horn Bike ($34): This next amplifier also packs a healthy environment punch. If you like to bike, for recreation or for your commute, this is the perfect way to add some music to that routine. Biking with headphones doesn’t work: You get all tangled up, and you often can’t hear traffic or blaring horns over your playlist. The Horn Bike solves those problems. The eco-friendly and recyclable silicone case is shock-proof, scratch-proof, and washable and attaches to virtually any bicycle handlebars. As always, it’s important to be aware of your surroundings while biking and we don’t recommend trying to toggle songs or change the volume while en route.

3. Phonofone III ($195): On the less portable side, we’ve got the Phonofone III. This is definitely one that makes a statement. The elegant analog design adds to your decor while adding to your music’s volume (they claim the device can reach up to 60 decibels). Sleek and sophisticated, this amp is almost a piece of art as well as an effective sound-booster.

4. AirCurve ($15): This little device serves as a nice dock for your phone. It lets you slide your power cord through to charge while listening, or remove it to take the speaker on the go. Pumping up the volume by about 10 decibels, this inexpensive stand is a clear winner.

5. iBamboo (Temporarily Out of Stock): The simple, natural aesthetic of this speaker makes it an incredibly beautiful way to snag a nice, amplified sound. It embraces the inherent resonance of bamboo to turn this single material into an environmentally-friendly and efficiently produced way to improve the volume coming from your iPhone speakers.

6. Tembo Trunks ($40): These waterproof, shock-proof, and dust-proof speakers are collapsible and easy to take just about anywhere. The company says they offer up to 80 decibels of clear sound. They’re pretty perfect for the music lover on the go because they’re light, flexible, and stackable. They even claim to save battery life versus using your internal iPhone speaker.

Which amplifier is just right for your next impromptu dance party? Let us know in the comments below or come talk to us over on Twitter.