There are several things wrong with Cause for Alarm, all of which contribute to a less than satisfying experience. Loretta Young is, to put bluntly, completely unconvincing as the wife of Barry Sullivan. Her attempts at portraying panic and something approaching a nervous breakdown just make her seem weak minded and vague. This is a role that would have suited a noir queen like Ida Lupino who can sustain a level of acting and intensity entirely suitable to this kind of plot. Sullivan, by contrast, gives his usual excellent performance - as far as it can extend given the inadequate script.
Another problem with this film is the storyline. Sullivan's descent into paranoia is too abrupt, too blunt to be really convincing or effective. During the flashback there are hints of a darkness in his soul and a cruelty, one which his future wife Eleen is entirely unaware of. Suddenly we are asked to attribute his mania to an overdose of heart medicine. This inconsistency is illogical, detracting from the menace established by his character in the early scenes.
On the plus side, a noir set in and around the home (and especially the home that isn't that of a policeman, as in say The Big Heat) is a good idea, with a lot of potential. The kitchen or the living room can be just as dangerous and claustrophobic as the mean streets outside. It's a shame that the Jones' home is not made more of as a source of menace. Sullivan's suspicions initially seem promising but he dies too quickly and make his accusations to easily to really satisfy.
The standouts in the cast is Irving Bacon as the pedantic postman. His beautifully fussy performance, a finely honed affair of self importance and wariness, almost make the rest worth sitting through... In short Cause for Alarm is no real cause for celebration. A shame, especially as Garnett also directed the classic The Postman Always Rings Twice.