I am having a lot of fun looking up stuff for you to do btw whilst in San Francisco especially because you said tech stuff and well offbeat activities which are aplenty in SF 

Source: NateKharrl/Flickr
So first some science/tech/gadgety things to do for you include:
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A visit to the California Academy of Sciences at Golden Gate Park is bound to blow your mind away. Check out the rainforest biodome in the photo above. The aquarium apparently is something else to watch. You gotta experience "Night Life" at the Steinhart Aquarium on Thursdays from 18:00-22:00. With an admission fee of $25, this is one place that will leave you wanting more. Check out the Events page for more information.
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Visit San Francisco's science and perception museum, the Exploratorium. Crawl and slide through the San Francisco Exploratorium's tactile dome in the dark using all your senses but sight.
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Why on earth am I recommending the SF Children's Museum to you? Because I reckon it would be fun to explore the kid in you. Zeum is art and tech museum for children. With $10 for admission, this might just be fun to explore.
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Check out the Cartoon Art museum which is home to 6,000 pieces of original and cartoon and animation art. It is located downtown in San Francisco’s Yerba Buena cultural district
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Hang out at DNA Lounge in SF -This is a late-night, all ages nightclub in the SoMa district of San Francisco owned by Jamie Zawinski, a former Netscape programmer. Check out their calendar (not yet updated with May events unfortunately)
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Check out Musée Mécanique one of the world's largest (over 200) privately owned collection of coin-operated mechanical musical instruments. Located at Fisherman's Wharf, admission is free. Check them out here.
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If you are in Mountain View and know someone at Google, bribe your way into the Google Cafetaria

Other fun, offbeat stuff to do
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Check out Camera Obscura which produces spectacular, 360 degree live images of the Seal Rock area
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Get a chocolate fix at Ghirardelli Square- Sit near the fountain sipping the best hot chocolate in San Francisco
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Check out the Community Music Centre at the Mission. They have music concerts that are free - check out their schedule here.
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Catch a movie at the historic Castro Theater- Independent films, classic films and more thought-provoking celluloid at San Francisco's famous Castro Theater
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Become an actor - step into Keanu Reeve's shoes with Point Break Live! Each performance features a new, unrehearsed actor in the protagonist role of 'Keanu', reading their lines from cue-cards delivered by a production assistant.
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Go out to Fort Funston and watch hang gliders at eye level. You are on top of a 150' clif. They are on top of 150' of air. If you are really adventurous sign up for a tandem flight.
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You are in San Francisco and you don't do Alcatraz. That would be a crime against history. Check out prices for cruises to Alcatraz here
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Check out what locals are chomping on in San Francisco with a Food Tour to satiate your senses. It doesn't come cheap at $59 but I am sure your stomach is going to be satisfied

Check out what readers of NY Times have recommended you do while in SF and more here as well.
I also thought you might like to see what I had recommended previously to a query on San Francisco. Please read here for more.
If you need any more help in terms of restaurants and attractions around San Francisco, please let me know and I will be more than happy to help.
Have fun on your trip
Kirti