Diacetyl Rest

After 8 days of fermentation I brought my lager up to room temp over 40 hours or so, but now the airlock is more active than it ever was during the first 8 days. I pitched a starter to a well aerated wort and my lag time was only 10 hrs.
I know I need to check the gravity during fermentation to truly check when its done, but I don't really have a sterile way of doing that.

Is this a sign that my fermentation wasn't near completion? What should I do?

I don't know- I usually primary around 12 days and then check the sg. If it's about 75% finished, I do the d-rest if it's needed. All you need to do to check the sg is to sanitize a turkey baster, take the lid off and pull a sample out into your hydrometer jar. That's really the only way to know. If it's done, then I do the secondary by racking and then gradually dropping the temperature until it's at 34 degrees.

Do lagers take typically take longer to ferment than ales?

Absolutely. I allow approx 12 days for primary, like I said, but it can definitely be longer than that. That's why sg readings are so important- no way to tell just by airlock activity how far long the fermentation is. And lager yeasts are bottom fermenting, so krausen isn't reliable either.

For some lager yeasts, a d-rest isn't necessary. For some, it's crucial. I also do a longer secondary, depending on the yeast strain I'm using. It's always good to follow the manufacturer's instructions on their website for each yeast strain you use when you do lagers. They require different temps, different lengths of time, a d-rest, ect.

Also, when you brought that up to room temp, you dropped the solubility of CO2 a lot. I would suspect that a lot of what you were seeing was CO2 that was trapped from fermentation being released due to the higher temperature.

Excellent point, thanks for all the help everybody