The police don't need a warrant to search a house where 3 out of 4 occupants are on probation. Yes, they may handcuff you during the search to insure officer safety. Frankly, for your own good, you shouldn't be living with 3 meth heads.
I must agree with Mr. Kaman's life advice. I would move or, if possible, arrange for the roommates to move.
As to the search. Cops can do probation searches where it is provided for in the probationer's terms and conditions. Search of your locked room to which your roommates have no access, I think is a different issue. [However, I am not certain it is worth the funds it would take to pursue an action]. To peusue that , call an attorney who regularly handles 1983 and ppolice law suits.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.
Below is the link to the Bolivar case which would be good background reading. You have two basic concerns (and a lot of others)
Bolivar teaches that even where there is a locked safe, and even where the non parolee was caught with the combination, because the safe was on the parolee's premises, the parolee was considered to have a reasonable cause to have access to it. Turning it around, even with a locked room, it cannot be firmly established that your roommates do not have a key. (and that you don't have a key to their area.
Second, if contraband is found you can easily be charged based upon the presumption stated above. The only way to get out of it without a full trial, or without a sympathetic DA, might be for the other 3 guys to confess and confess in such a way that it is clear that you are not involved.
Third, the case of US v. Davis is also linked and it has some interesting language at paragraph 22 on the differences (slight) between parolees and probationers. Paragraph 26-30 is a review of the now unimportance of the previous rule in which officers used to ask "is this yours", "is this theirs"? They don't seem to care anymore.
Fourth, if any of your room-mates angers one of the searching officers, it will spill onto you.
Curt Harrington Patent & Tax Law Attorney Certified Tax Specialist by the California Board of Legal Specialization PATENTAX.COM This communication is general information and not legal advice, and does not create an attorney-client relationship. This communication should not be relied upon as any type of legal advice. Please note that no attorney-client relationship exists between the sender and the recipient of this message in the absence of either (1) a signed fee contract and (2) remission of an agreed-upon retainer. Absent such an agreement and retainer, I am not engaged by you as an attorney, nor is any other member of my law firm.